Thanks Gerry, it seems Mach3 is a minefield of issues from version to version.

I do use the M6 so I will not downgrade to the very early version.

Not really sure what to do now TBH.

I will be back up and running this weekend, I will re-run the same code that failed and see what happens, only the motor has been changed so nothing that will alter the code execution. This might work or fail, if it fails I will try V028 instead.

I did ask CS-Labs about Mach4 but they advised holding fast until their new re-written plugin is published in the not too distant future.