This error occurs when IIS goes to SQL Server and tries to login with credentials that do not have proper permissions. This error can also occur when replication or mirroring is set up.
To resolve this error, Download and install Management Studio Express and then open the Unify Database.
Go to SQL Server >> Security >> Logins and right click on NT AUTHORITY\NETWORK SERVICE and select Properties
In newly opened screen of Login Properties, go to the “User Mapping” tab. Then, on the “User Mapping” tab, select the desired database – especially the database for which this error message is displayed. On the lower screen, check the role db_owner. Click OK.
In almost all such cases, this should fix your problem. If not, feel free to call in to Webgility Support at 877 753 5373 ext 3.