When you cleaned up your previous installations, did you do it as specified here? http://wiki.phoenixviewer.com/fs_clean_install (That page is written for the Firestorm viewer, but it applies to the stock Linden Lab viewer as well) Also, did you see this post by Rolig Loon: media_plugin_cef.dll is part of your viewer.  It is installed automatically when you install the Linden Lab viewer or any of the third party viewers.  You will find it in the program files directory on your computer.  On