System.InvalidOperationException at crm logon

Today I had a service call with Microsoft CRM Support. After the import of an organization into a development system at a client, it stopped working. Trying to logon CRM via web client fails with error message:

System.InvalidOperationException: ExecuteNonQuery requires the command to have a transaction when the connection assigned to the command is in a pending local transaction. The Transaction property of the command has not been initialized.

The solution of this problem was quite simple (after the reason was found). The application pool of the system had insufficient rights for the organization database.

To get the system up and running again you have to

1. Identify the identity of the application pool
2. Ensure the app pool idenity has a sql user assigned for the organization database
3. Grant the app pool identity the right db_owner on the organization database
4. Restart IIS