alot of possibility
but the most common one is
1) uncompatible version of W3
2) user using uncompatible Maphack
3) network issues - Firewall might be, Antivirus also might be

to tackle the issues are
1) copy new warcraft game to the hard disk from ppl that can play w3
2) Use the compatible Maphack - however it's unlikely to happen because not a lot of Maphack release that are compatible with the new version 1.22a..