THANKYOU Nick952
All is working again now.
Perhaps this option is turned on by default by the update.

As for the original subject;
Somewhere along the line Mach4 stopped freezing at the Tool Change code line and now passes through as previously.
The only thing I really fiddled with was the "T on M6 line is next tool" option mentioned by
gorf23
"I think if you go into mach4 config-tools and check T on M6 line is next tool it will not stop and ask for a tool change"

This was the way it was already set when it was freezing at the tool change line.
Perhaps fiddling with it had something to do with the preference "sticking" along the lines of the general computer "Turn it off and turn it on again" paradigm.

Anyhow,
Thanks to the contributors for your input.

Cheers,
Nicholas