“Why am I getting this error when I try to open a Client or Matter record through File Maintenance Manager or File Maintenance Matter Manager?”

Most likely this would be happening at a new site.  What we found was that the Security Groups did not have a Data View Profile.  

It may not need that Data View Profile filled out but try creating a default one by staying in Admin and go to Tables and Views on the left then Data View Profiles.  Click on New and just name it Default Profile. 

Example of error coming over to error inbox.