On my Windows XP PC with a old duo core CPU and 1GB RAM, I installed an AMD card over the weekend and then moved the card to my main PC. However, I didn't uninstall the Catalyst driver 13.12 that I installed for the test. Afterward, the YACoin qt wallet 0.4.2 couldn't start and gave me an "assertion failed" error. The problem vanished as soon as I removed Catalyst. Everything seems ok for me now. I'm just putting it here in case other people find it relevant.

Longer version of the error message: