Answer:
"Lab Instructors" group has been removed from the "Allow log on locally" policy.
Step-by-step explanation:
Based on the scenario being described within the question it can be said that the most likely problem would be that the "Lab Instructors" group has been removed from the "Allow log on locally" policy. This policy specifies the individuals or groups that are allowed access to the local computer network. Being removed from this policy would prevent access, just as is happening in this situation.