Start my app instead of Explorer but only app wan't

i wont to start my app instead of explorer but i have had a bad luck, i tried many apps path on the shell value, and all of them worked fine but only my application didn't work, and i don't know why, my apps normally starts without any problem. this is the path of the registry that i modified.

Navigate to HKEY_LOCAL_MACHINE>Software>Microsoft>Windows NT>CurrentVersion>Winlogon:shell

is there any thing that could cause this problem.