Just now I've got this error again. I can't tell surely, what was the reason, but I still suppose, that nothing special.
However I can give a hint. When I left my computer yesterday evening, everything was OK. Now I have not even made any srceenshot, only opened HS to view a screenshot made yesterday - and see this thumbnails bug. So we can conclude, that the cause of the error is not connected any way with screen capturing processes.
And, once more, my hypothesis, that the error appears itself independently of any user operation. Some kind of time-bomb in HS code
 

Support When it happens again, try to close or hide the thumbnails bar, then show it again (there is a check-box for it on the Setup ribbon tab), let me know if after that the check-boxes return to the normal size.

I've tried disable-enable-disable several times to be sure, but it had no any effect, sorry...

I finally traced this issue to desktop "theme" changes on Windows 7 (and maybe other versions of Windows). I fixed it in ver. 7.11.03 of HyperSnap, so please update your copy and the issue will be no more.
 
Before you upgrade, you could test that it still happens in an older version: have HyperSnap 7 running and opened in a window or minimized to the taks-bar or system tray. Right-click empty desktop and select "Personalize", then change the theme to anything else temporarily and when the change is done, look back at HyperSnap 7 window, the check-boxes should be huge and messed up. After an upgrade to 7.11.03 it should no longer happen.
 
Such theme changes sometimes happen even without your explicit action, e.g. if you start some game, it may change desktop theme to "basic" while the game runs, then back to "aero" when you exit the game. Other software may do this too, messing up the older versions of HyperSnap 7 in the process.
 
Greg