Index: t3lib/jsfunc.inline.js
===================================================================
--- t3lib/jsfunc.inline.js	(Revision 7070)
+++ t3lib/jsfunc.inline.js	(Arbeitskopie)
@@ -129,7 +129,7 @@
 	makeAjaxCall: function(method, params, lock) {
 		var max, url='', urlParams='', options={};
 		if (method && params && params.length && this.lockAjaxMethod(method, lock)) {
-			url = 'ajax.php';
+			url = TBE_EDITOR.getBackendPath() + 'ajax.php';
 			urlParams = '&ajaxID=t3lib_TCEforms_inline::'+method;
 			for (var i=0, max=params.length; i<max; i++) {
 				urlParams += '&ajax['+i+']='+params[i];
Index: t3lib/class.t3lib_tceforms_fe.php
===================================================================
--- t3lib/class.t3lib_tceforms_fe.php	(Revision 7070)
+++ t3lib/class.t3lib_tceforms_fe.php	(Arbeitskopie)
@@ -166,6 +166,9 @@
 	public function initializeTemplateContainer() {
 		t3lib_div::requireOnce(PATH_typo3 . 'template.php');
 		$GLOBALS['TBE_TEMPLATE'] = t3lib_div::makeInstance('frontendDoc');
+		$GLOBALS['TBE_TEMPLATE']->getPageRenderer()->addInlineSetting(
+			'', 'PATH_typo3', t3lib_div::dirname(t3lib_div::getIndpEnv('SCRIPT_NAME')) . '/' . TYPO3_mainDir
+		);
 
 		$GLOBALS['SOBE'] = new stdClass();
 		$GLOBALS['SOBE']->doc = $GLOBALS['TBE_TEMPLATE'];
Index: typo3/jsfunc.tbe_editor.js
===================================================================
--- typo3/jsfunc.tbe_editor.js	(Revision 7070)
+++ typo3/jsfunc.tbe_editor.js	(Arbeitskopie)
@@ -551,7 +551,23 @@
 			}
 		}
 		return false;
-	}	
+	},
+
+	/**
+	 * Determines backend path to be used for e.g. ajax.php
+	 * @return string
+	 */
+	getBackendPath: function() {
+		var backendPath = '';
+		if (TYPO3) {
+			if (TYPO3.configuration && TYPO3.configuration.PATH_typo3) {
+				backendPath = TYPO3.configuration.PATH_typo3;
+			} else if (TYPO3.settings && TYPO3.settings.PATH_typo3) {
+				backendPath = TYPO3.settings.PATH_typo3;
+			}
+		}
+		return backendPath;
+	}
 };
 
 function typoSetup	() {