I've seen this issue posted in these forums before as well, and this has happened twice to me now -- can't figure out a fix. What I've noticed is that when I run ComboFix just once on a computer, that seems to be what causes Keepass to stop working altogether and produce that error.
Also as a side note, if I run Rkill (this program stops processes running on your comp that could potentially interfere with other programs finding malware/viruses) it kills the Keepass setup process.
I've tried uninstalling Combofix, Keepass, and re-installing Keepass from the .exe or .zip file placed elsewhere on other drives or in dropbox etc, but nothing's working still. Not able to try from a USB stick yet as I don't have one, but that may be the fix. More than anything just wanted to make others aware that ComboFix seems to be the culprit of this error in this case.
KeePass requires .NET and maybe ComboFix breaks .NET?
Try repairing .NET, then run KeePass from the zip file, extracted to a temporary directory.
Gotcha, definitely has to do with .NET. Repairing .NET and running KeePass from zip extracted to a temp directory didn't work, but I did ultimately fix it by turning off .NET in control panel section of turning windows features on or off. I then updated my windows to 8.1 (since it needed to be anyway) and it essentially re-installed .NET with it right after it updated. Now KeePass works. Thanks for your help!