"http://localhost/reports" - "HTTP Error 503. The service is unavailable."

Problem:

Earlier "http://localhost/reports" worked fine in Windows 7. But, today, "HTTP Error 503. The service is unavailable."

Solution: 

After deleting the testUser (standard account) from User Account, it works fine. This is why: Although it appears that I have logged in with the admin account, not the testUser account, but I have used the testUser account for testing before. The system for some reason has used the cached testUser account, instead of the desired admin account in opening the report manager.