diff --git a/SeedDMS_Core/Core/inc.DBAccessPDO.php b/SeedDMS_Core/Core/inc.DBAccessPDO.php
index c6e76dbb1..d3f5cbd80 100644
--- a/SeedDMS_Core/Core/inc.DBAccessPDO.php
+++ b/SeedDMS_Core/Core/inc.DBAccessPDO.php
@@ -532,13 +532,13 @@ class SeedDMS_Core_DatabaseAccess {
 						"GROUP BY `tblDocumentReviewLog`.`reviewID` "; //.
 //						"ORDER BY `maxLogID`";
 			}
-            if (!$this->_ttreviewid) {
+			if (!$this->_ttreviewid) {
 				if (!$this->getResult($queryStr))
 					return false;
 				$this->_ttreviewid=true;
 			}
 			else {
-                if (is_bool($override) && $override) {
+				if (is_bool($override) && $override) {
 					if (!$this->getResult("DROP TABLE IF EXISTS `ttreviewid`"))
 						return false;
 					if (!$this->getResult($queryStr))
diff --git a/inc/inc.ClassExtensionMgr.php b/inc/inc.ClassExtensionMgr.php
index d49ba02ef..3705465f2 100644
--- a/inc/inc.ClassExtensionMgr.php
+++ b/inc/inc.ClassExtensionMgr.php
@@ -51,6 +51,12 @@ class SeedDMS_Extension_Mgr {
 	 */
 	protected $cachedir;
 
+	/**
+	 * @var array $configcache cached result of checkExtensionByName()
+	 * @access protected
+	 */
+	protected $configcache;
+
 	/**
 	 * @var string[] $errmsg list of error message from last operation
 	 * @access protected
@@ -104,6 +110,7 @@ class SeedDMS_Extension_Mgr {
 	 * is given
 	 */
 	public function __construct($extdir = '', $cachedir = '', $reposurl = '', $proxyurl='', $proxyuser='', $proxypass='') { /* {{{ */
+		$this->configcache = [];
 		$this->cachedir = $cachedir;
 		$this->extdir = $extdir;
 		$this->reposurl = $reposurl;
@@ -325,48 +332,66 @@ class SeedDMS_Extension_Mgr {
 		return $ret;
 	} /* }}} */
 
+	public function checkExtensionByDir($dir, $options = array()) { /* {{{ */
+		$this->errmsgs = array();
+
+		if(!file_exists($dir)) {
+			if(!file_exists($this->extdir.'/'.$dir))
+				return false;
+			else
+				$dir = $this->extdir.'/'.$dir;
+		}
+		if(!file_exists($dir."/conf.php")) {
+			$this->errmsgs[] = "Missing extension configuration";
+			return false;
+		}
+		include($dir."/conf.php");
+		if(!isset($EXT_CONF)) {
+			$this->errmsgs[] = "Missing \$EXT_CONF in configuration";
+			return false;
+		}
+		$extname = key($EXT_CONF);
+		if(!$extname || !preg_match('/[a-zA-Z_]*/', $extname)) {
+			$this->errmsgs[] = "Extension has invalid or no name";
+			return false;
+		}
+
+		$extconf = $EXT_CONF[$extname];
+
+		if(!empty($extconf['language']['file']) && !file_exists($dir."/".$extconf['language']['file'])) {
+			$this->errmsgs[] = "Missing language file";
+		}
+		if(!empty($extconf['class']['file']) && !file_exists($dir."/".$extconf['class']['file'])) {
+			$this->errmsgs[] = "Missing class file";
+		}
+		if(!empty($extconf['icon']) && !file_exists($dir."/".$extconf['icon'])) {
+			$this->errmsgs[] = "Missing icon file";
+		}
+
+		if($this->errmsgs)
+			return false;
+
+		return self::checkExtensionByName($extname, $extconf, $options);
+	}
+
 	/**
 	 * Check content of extension directory or configuration of extension
 	 *
 	 * @param string|array $dir full path to extension directory or extension name
 	 * or an array containing the configuration.
-	 * @param boolean $noconstraints set to true if constraints to local seeddms
-	 * installation shall not be checked.
+	 * @param array $options array with options elements 'noconstraints' and 'nofiles'.
+	 * Set 'noconstraints' to true if
+	 * constraints to local seeddms installation shall not be checked. Set 'nofiles'
+	 * to true to turn off checking of files
+	 * @return boolean true if check was successful, otherwise false
 	 */
-	public function checkExtension($dir, $options=array()) { /* {{{ */
-		$this->errmsgs = array();
-
-		if(is_string($dir)) {
-			if(!file_exists($dir)) {
-				if(!file_exists($this->extdir.'/'.$dir))
-					return false;
-				else
-					$dir = $this->extdir.'/'.$dir;
-			}
-			if(!file_exists($dir."/conf.php")) {
-				$this->errmsgs[] = "Missing extension configuration";
-				return false;
-			}
-			include($dir."/conf.php");
-			if(!isset($EXT_CONF)) {
-				$this->errmsgs[] = "Missing \$EXT_CONF in configuration";
-				return false;
-			}
-			$extname = key($EXT_CONF);
-			if(!$extname || !preg_match('/[a-zA-Z_]*/', $extname)) {
-				$this->errmsgs[] = "Extension has invalid or no name";
-				return false;
-			}
-
-			$extconf = $EXT_CONF[$extname];
-		} elseif(is_array($dir)) {
-			$extconf = $dir;
-			/* If just the configuration is passed, then there is no way to check
-			 * for existence of files.
-			 */
-			$options['nofiles'] = true;
+	public function checkExtensionByName($extname, $extconf, $options=array()) { /* {{{ */
+		if(isset($this->configcache[$extname])) {
+			return $this->configcache[$extname];
 		}
 
+		$this->errmsgs = array();
+
 		if(!isset($extconf['constraints']['depends']['seeddms'])) {
 			$this->errmsgs[] = "Missing dependency on SeedDMS";
 		}
@@ -382,17 +407,6 @@ class SeedDMS_Extension_Mgr {
 		if(!isset($extconf['author'])) {
 			$this->errmsgs[] = "Missing author";
 		}
-		if(!isset($options['nofiles']) || $options['nofiles'] == false) {
-			if(!empty($extconf['language']['file']) && !file_exists($dir."/".$extconf['language']['file'])) {
-				$this->errmsgs[] = "Missing language file";
-			}
-			if(!empty($extconf['class']['file']) && !file_exists($dir."/".$extconf['class']['file'])) {
-				$this->errmsgs[] = "Missing class file";
-			}
-			if(!empty($extconf['icon']) && !file_exists($dir."/".$extconf['icon'])) {
-				$this->errmsgs[] = "Missing icon file";
-			}
-		}
 
 		if(!isset($options['noconstraints']) || $options['noconstraints'] == false) {
 			if(isset($extconf['constraints']['depends'])) {
@@ -446,9 +460,11 @@ class SeedDMS_Extension_Mgr {
 		}
 
 		if($this->errmsgs)
-			return false;
+			$this->configcache[$extname] = false;
+		else
+			$this->configcache[$extname] = true;
 
-		return true;
+		return $this->configcache[$extname];
 	} /* }}} */
 
 	static protected function rrmdir($dir) { /* {{{ */
@@ -498,7 +514,7 @@ class SeedDMS_Extension_Mgr {
 //		exec($cmd);
 
 		/* Check if extension is complete and fullfills the constraints */
-		if(!self::checkExtension($newdir)) {
+		if(!self::checkExtensionByDir($newdir)) {
 			self::rrmdir($newdir);
 			return false;
 		}
diff --git a/inc/inc.ClassUI.php b/inc/inc.ClassUI.php
index e11591b8f..638848884 100644
--- a/inc/inc.ClassUI.php
+++ b/inc/inc.ClassUI.php
@@ -56,7 +56,7 @@ class UI extends UI_Default {
 		$decorators = array();
 		foreach($extMgr->getExtensionConfiguration() as $extname=>$extconf) {
 			if(!$settings->extensionIsDisabled($extname)) {
-				if($extMgr->checkExtension($extconf)) {
+				if($extMgr->checkExtensionByName($extname, $extconf)) {
 					if(isset($extconf['decorators'][$class])) {
 						$filename = $settings->_rootDir.'ext/'.$extname.'/decorators/'.$theme."/".$extconf['decorators'][$class]['file'];
 						if(file_exists($filename)) {
@@ -73,7 +73,7 @@ class UI extends UI_Default {
 		$httpbasedir = '';
 		foreach($extMgr->getExtensionConfiguration() as $extname=>$extconf) {
 			if(!$settings->extensionIsDisabled($extname)) {
-				if($extMgr->checkExtension($extconf)) {
+				if($extMgr->checkExtensionByName($extname, $extconf)) {
 					/* Setting the 'views' element in the configuration can be used to
 					 * replace an existing view in views/bootstrap/, e.g. class.ViewFolder.php
 					 * without providing an out/out.ViewFolder.php. In that case $httpbasedir
diff --git a/inc/inc.Extension.php b/inc/inc.Extension.php
index 004ae40ad..407bca391 100644
--- a/inc/inc.Extension.php
+++ b/inc/inc.Extension.php
@@ -26,9 +26,10 @@ $version = new SeedDMS_Version;
 foreach($extMgr->getExtensionConfiguration() as $extname=>$extconf) {
 	if(!$settings->extensionIsDisabled($extname)) {
 		$disabled = true;
-		if($extMgr->checkExtension($extconf)) {
+		if($extMgr->checkExtensionByName($extname, $extconf)) {
 			$disabled = false;
 		} else {
+			$settings->disableExtension($extname);
 		//	echo $extMgr->getErrorMsg();
 		}
 		/* check for requirements */
@@ -42,30 +43,30 @@ foreach($extMgr->getExtensionConfiguration() as $extname=>$extconf) {
 		}
 		 */
 		if(!$disabled) {
-		if(isset($extconf['class']) && isset($extconf['class']['file']) && isset($extconf['class']['name'])) {
-			$classfile = $settings->_rootDir."/ext/".$extname."/".$extconf['class']['file'];
-			if(file_exists($classfile)) {
-				include($classfile);
-				$obj = new $extconf['class']['name']($settings, null, $logger);
-				if(method_exists($obj, 'init'))
-					$obj->init();
+			if(isset($extconf['class']) && isset($extconf['class']['file']) && isset($extconf['class']['name'])) {
+				$classfile = $settings->_rootDir."/ext/".$extname."/".$extconf['class']['file'];
+				if(file_exists($classfile)) {
+					include($classfile);
+					$obj = new $extconf['class']['name']($settings, null, $logger);
+					if(method_exists($obj, 'init'))
+						$obj->init();
+				}
 			}
-		}
-		if(isset($extconf['language']['file'])) {
-			$langfile = $settings->_rootDir."/ext/".$extname."/".$extconf['language']['file'];
-			if(file_exists($langfile)) {
-				unset($__lang);
-				include($langfile);
-				if(isset($__lang) && $__lang) {
-					foreach($__lang as $lang=>&$data) {
-						if(isset($GLOBALS['LANG'][$lang]))
-							$GLOBALS['LANG'][$lang] = array_merge($GLOBALS['LANG'][$lang], $data);
-						else
-							$GLOBALS['LANG'][$lang] = $data;
+			if(isset($extconf['language']['file'])) {
+				$langfile = $settings->_rootDir."/ext/".$extname."/".$extconf['language']['file'];
+				if(file_exists($langfile)) {
+					unset($__lang);
+					include($langfile);
+					if(isset($__lang) && $__lang) {
+						foreach($__lang as $lang=>&$data) {
+							if(isset($GLOBALS['LANG'][$lang]))
+								$GLOBALS['LANG'][$lang] = array_merge($GLOBALS['LANG'][$lang], $data);
+							else
+								$GLOBALS['LANG'][$lang] = $data;
+						}
 					}
 				}
 			}
 		}
-		}
 	}
 }