Hi, I have been having an issue that's been driving me insane for the last two days, after much googling (and binging of course 
)
I am still at a loss for a solution. If anyone has come across this before or even able just to point me in a direction I haven't considered I'd be very grateful.
SETUP
Website deployed on Domain A, users and service account on Domain A, users on Domain B.
ISSUE
Users on domain A (same as website) can authenticate successfully to the website through windows authentication. Users on domain B cannot access the site. 
AD setup
Domain A Usergroup - website references this group
Inherits Domain A Universal group
Inherits Domain B Usergroup
Log entries
IIS logs: User from Domain B receives a 401.2 error
Security Logs: User from Domain B logs in successfully, however immediately afterwards there are two log entries stating the service account on Domain A fails with an invalid username and password.