You are unable to configure the MSA on the Security Settings > Exchange Group > Configure page of console of WFBS running on IIS 6.0.
The issue occurs because the access rights assigned to the Internet Information Services (IIS) 6.0 user account is low-level.
On the other hand, the Local Service user account also has low-level access rights, but is more useful in situations that do not require access to resources on remote computers.
Configuring application pools to run under the Local System user account will provide greater user access rights than the Network Service or Local Server user accounts.
To resolve the issue, create a new application pool for the SMEX website with "Local System" as the privilege:
- Open IIS Manager and double-click the local computer icon.
- Right-click Application Pools and select New > Application Pool.
- Select "Use default settings for new application pool".
- Click OK.
- Return to the local computer icon and find the new Application Pool.
- Right-click the Application Pool and select Properties.
- Click the Identity tab and choose Predefined.
- Select Local System.
- Click OK.
- Expand the Web Sites folder.
- Right-click SMEX Web Site and select Properties.
- Click the Home Directory tab and select the created Application Pool.
- Click OK when the Inheritance Overrides prompt shows up.
- Stop and restart the SMEX virtual web site.