Cygwin Not showing right groups.

1. First check whether the group u want to c is the primary group for that user in the Domain. If not Make it the Primary group.
2. Next check whether the local group policies have been updated. Without that Cygwin wont be able to know which group the user is referring to.
3. Remake the passwd and the group files of cygwin using mkpasswd and mkgroup command.
Without this Changed data will not be updated into Cygwin authentications and the error will still remain there.