Click on the OPTIONS button, then on the DISK tab. Click the Clear Unused Cache Files button. Then try exporting once again. If no luck, follow these steps...
1. Click FILE|SAVE AS PORTABLE PROJECT.
2. Zip all the files that result.
3. Upload the ZIP file to a free server, such as MS OneDrive, Google Drive, DropBox, etc.
4. Make the link to the file public and post it here and someone will check out your project.
You might also try installing the latest VP, though export choices may be limited. Retain your 5.21 install file in case you want to revert to that version.