the issue is most likely the users permissions in the permissions databases. Microsoft has 4 different Membership/Identity sdks. Your code looks old so it's most likely one of the deprecated sdks. Either the original Asp.net 2.0 Membership or the Universal drivers. It could also be completely custom.
the original Membership supported using Active Directory or sqlserver to store permissions. The Universal drives allowed custom databases. To help identify your code we need your web.config info. any section in the following list:
- authentication
- anonymousIdentification
- membership
- profile
- roleManager