Suddently config menu won't allow me to save (apply button greyed out) and it changed the T on M6 selection to use T for next tool upon start up. Need to change it back to T is current tool on M6 line, but the config won't save. Any suggestions are welcomed. Screen set is normal and all functions are working otherwise. Looked in the machine.ini file to manually change this but can't locate it.

I can confirm what SWIFTYJ said to repair this. Replace parameters.ini file in your current profile with your backup. To confirm it is this file simply open it, if it's blank then it was corrupted. First remove your blank file or give it a different name temporarily then paste your backup and...RESTART Mach 4.