Spy++ not working, but Spy++(64-bit) is?

I am writing an application in C# that sends keytrokes to another application. My code has worked before so this is no problem for me.

The thing is that the code actually does not work and neither does Spy++. On the other hand Spy++(64bit) does work so I am thinking there is a program which is globally hooking it.

I am running Win7 64bit and already tried to restart and disabled many programs but still no progress.

Anyone has an idea? Thanks.

PS: Do the both Spy++ versions use different hooking techniques?