For a while now I've had this reproducible error:
If I try to open any file (so regardless of its extension) that has a % in its name, regardless of the method of opening (click on it in Explorer, open it manually in the command prompt etc.), the program which is used to send the request (Explorer and cmd.exe, in the previous examples) would crash 100%.
Does anyone know the exact mechanism/sequence Windows uses to open a file? I could help out with debug information that way.

notepad.exe blub%.txt, which skips a lot of your described steps, shouldn't that narrow it down? – Buote Xu Apr 28 '12 at 10:24SDHook32.dll, which somehow couldn't deal with the filename. – Buote Xu Apr 28 '12 at 10:55