If I drag an MP4 to a new timeline or go file->import and point to the file, I get "The activation code is incorrect. Please make sure it has been entered correctly or contact the MAGIX customer service."
I've been able to open these same files in Vegas before. In another fresh install of Vegas on another machine, when I imported the MP4, I got a message that AAC was successfully activated. So something on this installation isn't allowing AAC to be activated?