TincyMCE not displaying preview, only displays code - solved

I recently (3 weeks ago) logged into my site manager and found that TinyMCE was no longer displaying the page preview but it would display the code.

I had this problem in IE, Chrome, Firefox and Safari. Updating to the latest Evo didn't work either.

I finally had some time to sort it out and it turned out to be some of the custom plugins under Tools-> Configuration-> Interface & Features.

I setup my plugins based on a post here or on another site and they worked fine for several years and Evo revisions.

My original plugins were "safari,spellchecker,pagebreak,style,layer,table,save,advhr,advimage,advlink,emotions,iespell,insertdatetime,preview,media,searchreplace,print,contextmenu,paste,directionality,fullscreen,noneditable,visualchars,nonbreaking,xhtmlxtras,template,imagemanager,filemanager"

The display problem seems to be caused by the imagemanager and filemanager plugins.

The preview was also displaying video links to Youtube as a blank Yellow square with the Flash logo in the middle - removing "media" from the plugin list solved that issue.

I don't have the time to investigate why but thought this may help someone.