This issue you have described is generally caused by a corrupted Video/Image Bin file. You will need to remove this file since there isn't a way to fix it. This will clear your entire Video/Image Bin, so you will need to re-import your media, but any media already linked to presentations won't be affected.
ProPresenter 5
1. Open ProPresenter 5.
2. Open Preferences (click on ProPresenter 5 in the top left of the screen and come down to Preferences).
3. Click on the General Tab.
4. Click on the Magnifying Glass under "Application Data". This will open a Finder window.
5. Switch back to ProPresenter and close (quit) the program.
6. Now, back in the Finder window, open the ProPresenter5 folder.
7. Locate media.pro5pl and drag it to your Desktop.
8. Launch ProPresenter 5.
ProPresenter 6
1. Open ProPresenter 6.
2. Open Preferences (click on ProPresenter 6 in the top left of the screen and come down to Preferences).
3. Click on the General Tab.
4. Click on the Magnifying Glass under "Support Files". This will open a Finder window.
5. Switch back to ProPresenter and close (quit) the program.
6. Now, back in the Finder window, open the ProPresenter6 folder.
7. Locate media.pro6pl and drag it to your Desktop.
8. Launch ProPresenter 6.
If the program opens, you can delete the media.pro5pl/media.pro6pl file from your desktop since this the program opening confir