I am having strange issue with my SQL 2008 R2 Server. We have an active-active cluster with 2 different instances running on it. On one of the instance which is installed recently, when I add windows users and assign db_reader & db_writer permissions but users are not able to write anything to database. We have similar setup in another location where everything works fine as expected. I have compared all permissions and roles. It is not a complex permissions to miss anything. No problem for users with sysadmin permissions.
At the moment I don't have any clue whats wrong? Is SQL 2008 R2 installation could be corrupted or some components missing?? Any help is greatly appreciated.