NT Authentication problem

[OldSkoolSkater]

I am currently building up Enterprise ready to migrate
from SI7.5 and after installing Enterprise selected NT authentication to be used.
All has been fine until today, when I went to change the option:
"Assign each added NT alias to an account with the same name"
to:
"Create a new account for every added NT alias"

When I clicked on update I received the error message:

Error updating Windows NT authentication properties: NT Authentication failed to verify the mapped groups. If the problem persists, please delete and re-map into Crystal all
currently mapped groups.

Following the instructions in the message I deleted the global NT group that Enterprise had been mapped to, and then tried to create it. I clicked on update after adding the group and the error message popped up again.

I have access to the CMC using the admin enterprise authentication account, and currently the only NT group that is mapped to Enterprise is the default 'crystal NT users' local group.
It seems that if I try to make any changes under this tab and then update them, I just get the error message.
Any ideas??

Cheers

Steve