Error in: Show or Hide Fields

Dear gINT community,

For the last weeks I have been banging my head against the wall to figure out how I can resolve the following error. In my lithology tab I would like to hide some fields, hence I go to Tables > Show or Hide Fields and the following message pops up:

Invalid procedure call or argument

MainCmd.CmdControl

 MainCmd.CmdExecute CmdID: 610 'Show or Hide Fields' 

 appInput.CmdControl: gINT8a

In the point tab and project tab I have no problem with the "Show or Hide Fields" command. Does anyone know how I can resolve this error? 

Thank you,

Thomas