I am getting following error each time I tried to select database. The database 'DB Name' is not accessible. (Microsoft.SqlServer.Express.ObjectExplorer) Note: My OS is Win Vista. When I tried to open SQL Mgmt Studio as Run as administrator than I can able to access database properly. Any idea why it is giving error. I am also getting following error when my asp.net application is trying to access database. Cannot open database "DBName" requested by the login. The login failed. Login failed for user 'PCName\abcd'. I am not very good with SQL Server, please let me know how to create user and grant them permission in case that is what causing the problem. Thanks.