It's not grayed out on your screen cap. Is that a different system?

Are other options grayed out?  Not sure why just the extension would be and not other options. If they all are, the config file may be in a read only folder or wrote protected, etc.

You could recreate the config from a different system and copy the D6.INI file to the system where you need to run it from.

What version of D6 are you running?  Most folks don't ever upgrade the COMM programs...there's little need...once configured, they just work. However I always try to keep them current. Maybe try a newer version.