What version of VP is being used? What is is the resolution of the bulk of the source files? And, as Nat queries, what are the export settings?
The best way to track this down is to share the project, if it's not more than a few GB. This doesn't take long, isn't difficult and can be private.
Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
If it contains sensitive material link it in a personal message (PM). Click the envelope above. It won't be passed on or retained. Use FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to get a shareable link to post.