You might get more advice on an Adobe forum but what I'd try first is... Export a master file of your timeline to learn if the issue is with the export or with the compression. If it works then compress that file separately (using Handbrake or whatever you like). If that compression works then your issue is with PP or your timeline itself. You can then try exporting sections of your timeline with H.264 compression to see if it's a particular part of the timeline that is problematic. More experienced PP folks might offer better suggestions on deleting preferences and such. I actually cut in FCPX so my advice is more generic NLE advice. Best of luck.