Have you solved this problem yet? There is a known problem with EPiFields in EPiServer 4.40/4.41, so if you are running one of those versions, here is what happens and how to solve it: When EPiFields is installed, it replaces one of the EPiServer editor's javascript files with a new file. This was necessary in pre-4.40 versions to fix a problem that occured when the editor was opened in dialogs. In 4.40 this is not needed anymore. In fact, when the EPiFields installer replaces the same script file in 4.40/4.41 it only causes problems. To fix the problem, just restore the original 4.40/4.41 script file on your site. The file in question is /Util/javascript/Editor/StartupScript.js and you can find the original file in the EPiServer download directory ("C:\Program Files\EPiServer4\Download").