compress or encrypted exe files.

[DABhand]

Olly is a debugger, and most protected wrapped executables will notice it running and either give your debugger a hard time by crashing the game or give you scrambled assembly.

I know its nice for breakpoints etc and tracing, but ideally you would need an unwrapped executable or somehow remote debug it.

Still Cheat Engine has a handy debugger of sorts, not good like olly but at least you can get somewhere with it.