well that's probably a virus, which i still can't pinpoint, or find a solution for 1 - my home pc was infected and it gave 0xc000007b error (initialization error) something like that to alll .net built assemblies 2 - now i have my pc at work who is infected, and gives me the error you just described. Now can you confirm that when you rebuild one of your own assemblies, and try to run it ...it runs correctly and after you close it, a couple of minutes, the file size changes just like that, and the problem starts? if you insert a USB drive, you'll have two infected files on it, they are hidden ... the first is 'autorun.inf' and the second is totally random, having an executable extension (such as .exe, .pif, ......)?