We've finally found the origin of the crash. Thank you very much cds904 !
The program crashed for cds904 and not for me, because we didn't do exactly the same thing.
cds904 clicked the "add" button, then selected "add from an existing video".
And personally, I selected the video from the "owned videos" box, then clicked the "add as owned" button.
This bug will be fixed with the next release of Coollector, but you can already download a fixed version:
http://www.coollector.com/Coollector.exe