Four suggestions...
Be sure that the video driver and Direct-X are up to date...
AMD / ATI users: http://support.amd.com/us/gpudownload/Pages/index.aspx Intel users: https://downloadcenter.intel.com/default.aspx nVidia users: http://www.nvidia.com/Download/index.aspx?lang=en-us Update DirectX: http://support.microsoft.com/kb/179113
Update to the most recent Videopad version. It's here. For licensed users upgrades are free for up to six months from purchase date. After that, VP will continue to fully function but a fee will be required in order to register the newest. Retain your old install file and registration info.
Is this a 4K Mp4 export? Click the Default Quality / Filesize link and choose the MPEG4 compressor, instead of the H264 default. 
If those measures don't help, please share your project (not the export). It's easy, takes little time and can be private. Someone will check it out and find the fix.
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 share it.