I made a program which sends Alt+Print key conbination using SendInput() function. The function works on 32 bit WinXP. My executable compiled for x86 also works on WinXP 64 bit. But when I use "AnyCPU" platform target, SendInput() still sends the keys, but they are not processed. After that, my left mouse button simulates my right one, until I press the right button. I also tested Shift+Print and it works the same. Could it be a bug in WinXP 64? I believe 32 and 64 bit dll versions should be identical. Anybody knows how to fix this?