diff --git a/CategoryTree.i18n.php b/CategoryTree.i18n.php
index 66cc524f..4707093a 100644
--- a/CategoryTree.i18n.php
+++ b/CategoryTree.i18n.php
@@ -33,6 +33,8 @@ $messages['categorytree-nothing-found']= 'nothing found';
 $messages['categorytree-no-subcategories']= 'no subcategories';
 $messages['categorytree-no-pages']= 'no pages or subcategories';
 $messages['categorytree-not-found']= "Category <i>$1</i> not found";
+$messages['categorytree-error'] = 'Problem loading data.';
+$messages['categorytree-retry'] = 'Please wait a moment and try again.';
 
 $messages['categorytree-show-list'] = "Show as list";
 $messages['categorytree-show-tree'] = "Show as tree";
diff --git a/CategoryTree.js b/CategoryTree.js
index 853f87c3..61cc9534 100644
--- a/CategoryTree.js
+++ b/CategoryTree.js
@@ -8,7 +8,11 @@
  * @copyright © 2006 Daniel Kinzler
  * @licence GNU General Public Licence 2.0 or later
 */
-    
+
+// Default messages if new code loaded with old cached page
+var categoryTreeErrorMsg = "Problem loading data."; 
+var categoryTreeRetryMsg = "Please wait a moment and try again.";
+
     function categoryTreeNextDiv(e) {
       var n= e.nextSibling;
       while ( n && ( n.nodeType != 1 || n.nodeName != 'DIV') ) {
@@ -55,10 +59,19 @@
       div.innerHTML= '<i class="CategoryTreeNotice">' + categoryTreeLoadingMsg + '</i>';
       
       function f( request ) {
+          if (request.status != 200) {
+              div.innerHTML = '<i class="CategoryTreeNotice">' + categoryTreeErrorMsg + ' </i>';
+              var retryLink = document.createElement('a');
+              retryLink.innerHTML = categoryTreeRetryMsg;
+              retryLink.onclick = function() {
+                  categoryTreeLoadChildren(cat, mode, div);
+              }
+              div.appendChild(retryLink);
+              return;
+          }
+
           result= request.responseText;
           result= result.replace(/^\s+|\s+$/, '');
-
-          if (request.status != 200) result= "<div class='error'> " + request.status + " " + request.statusText + ": " + result + "</div>";
           
           if ( result == '' ) {
                     result= '<i class="CategoryTreeNotice">';
diff --git a/CategoryTree.php b/CategoryTree.php
index 652c5714..a6ac584d 100644
--- a/CategoryTree.php
+++ b/CategoryTree.php
@@ -51,6 +51,7 @@ $wgCategoryTreeMaxDepth = array(CT_MODE_PAGES => 1, CT_MODE_ALL => 1, CT_MODE_CA
 $wgCategoryTreeExtPath = '/extensions/CategoryTree';
 $wgCategoryTreeDefaultMode = CT_MODE_CATEGORIES;
 $wgCategoryTreeCategoryPageMode = CT_MODE_CATEGORIES;
+$wgCategoryTreeVersion = '1';
 
 /**
  * Register extension setup hook and credits
diff --git a/CategoryTreeFunctions.php b/CategoryTreeFunctions.php
index 7b61557c..1061f333 100644
--- a/CategoryTreeFunctions.php
+++ b/CategoryTreeFunctions.php
@@ -23,7 +23,7 @@ class CategoryTree {
 	 * @param OutputPage $outputPage 
 	 */
 	static function setHeaders( &$outputPage ) {
-		global $wgJsMimeType, $wgScriptPath, $wgContLang, $wgCategoryTreeExtPath;
+		global $wgJsMimeType, $wgScriptPath, $wgContLang, $wgCategoryTreeExtPath, $wgCategoryTreeVersion;
 		efInjectCategoryTreeMessages();
 		
 		# Register css file for CategoryTree
@@ -31,7 +31,7 @@ class CategoryTree {
 			array( 
 				'rel' => 'stylesheet', 
 				'type' => 'text/css', 
-				'href' => $wgScriptPath . $wgCategoryTreeExtPath . '/CategoryTree.css' 
+				'href' => "$wgScriptPath$wgCategoryTreeExtPath/CategoryTree.css?$wgCategoryTreeVersion",
 			) 
 		);
 		
@@ -41,14 +41,14 @@ class CategoryTree {
 				array( 
 					'rel' => 'stylesheet', 
 					'type' => 'text/css', 
-					'href' => $wgScriptPath . $wgCategoryTreeExtPath . '/CategoryTree.rtl.css' 
+					'href' => "$wgScriptPath$wgCategoryTreeExtPath/CategoryTree.rtl.css?$wgCategoryTreeVersion" 
 				) 
 			);
 		}
 		
 		# Register main js file for CategoryTree
 		$outputPage->addScript( 
-			"<script type=\"{$wgJsMimeType}\" src=\"{$wgScriptPath}{$wgCategoryTreeExtPath}/CategoryTree.js\">" .
+			"<script type=\"{$wgJsMimeType}\" src=\"{$wgScriptPath}{$wgCategoryTreeExtPath}/CategoryTree.js?{$wgCategoryTreeVersion}\">" .
 			"</script>\n" 
 		);
 		
@@ -62,6 +62,8 @@ class CategoryTree {
 			var categoryTreeNothingFoundMsg = \"".Xml::escapeJsString(self::msg('nothing-found'))."\"; 
 			var categoryTreeNoSubcategoriesMsg = \"".Xml::escapeJsString(self::msg('no-subcategories'))."\"; 
 			var categoryTreeNoPagesMsg = \"".Xml::escapeJsString(self::msg('no-pages'))."\"; 
+			var categoryTreeErrorMsg = \"".Xml::escapeJsString(self::msg('error'))."\"; 
+			var categoryTreeRetryMsg = \"".Xml::escapeJsString(self::msg('retry'))."\"; 
 			</script>\n" 
 		);
 	}