Error loading file cabinet settings - invalid column name 'COLUMNNAME' after a DocuWare Upgrade. 

Check whether the columns displayed on the error message are existing on the database.
If the columns are not in the database, stop the Content Server and start the program DocuWare.Tools.CtServerUpgrader.exe" as Administrator (...\DocuWare\Content Server).
Since DW 7 you can find the DocuWare.Tools.CtServerUpgrader.exe in the Setup Components (...\DocuWare\Setup Components) directory. 

This programs checks if all tables and columns are created correctly in the database and creates them when they do not exist.

If the columns still cannot be created  - check in the folder columns of the affacted file cabinet within the database if the DWDOCID has been set as primary key. You can identify this if the parameter DWDOCID has a key symbol.
If the primary key was not created you can add it with the right mouse button.