Goto the folder which should look similar to this: ....Sony shared\File Formats\MP3\ Delete the file "mp3plug.dll" or do a search from the Start menu on the file "mp3plug.dll" and then delete it along with any othe files found with that name from the search results. Now reinstall Vegas 5. Something is probably corrupt with that driver DLL file, or something is messed up in your registry, where it's no longer pointing to the correct location of that file. Deleting that file will cause Vegas to reinstall it with a new one and change your registry information accordingly and all should work afterwards.