I am befuddled with a simple problem using Mach4.  I am unable to change the values of any of the DROs in the Probing Tab. For instance, I cannot modify any of the values in the Probing Settings tab.  Offset Number, G code: G, Slow measure feedrate,...  Am I missing something operationally and I am not supposed to be able to change them?   

Which build number of Mach4 are you using? Could you upload a copy of your screenset file?