It is hard to tell what is failing without more information so I will give you a self-help tip instead.
Check the security logs on the target machines. Have users try to load printers and mark the time. Examine the security logs to see what failed. Examine the system log to determine if any other clues point you in a productive direction.
MARK THE TIME so you know which entry coincides with your target event.
You disabled settings in the local computer policy for printing but what else did you modify? Did you document the alterations you made from the baseline?
Have you tried adding users to the print operators group (or Windows 7 equivalent)? Unfortunately, here at home I am running XP (non-Enterprise) and can’t try it out.