The 'free' (trial) version is the same as the licensed version, but has limitations. Install the latest version, but retain your licensed installer and code.
What version of Videopad is being used?
What are the export settings?
How long is the project?
What is the resolution of the bulk of the source files?
Try to export at a lower resolution. Try it as an AVI with the MPEG4 compressor.
Please upload and share the PORTABLE project folder (not the export). This is simple, quick and can be private. Just follow the PORTABLE project instructions here...
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. Someone will check it out.