Clive
I've just read post #3 and to me it does not sound like joining FOR and DCM is running the spindle all the time. Have a read and see if you agree.

Mark,
When you connected FOR and DCM the spindle briefly accelerated then cut out. It remained stationary until you disconnected FOR and DCM at which point nothing happened until the electronics had 'spooled down' to a low rpm at which point the spindle burst into life and tracked the speed down to zero. As if there is a dead spot above a very low rpm at which the spindle will not turn. Is this what you observed?

If I got this wrong please carry on. If not suggests VFD is faulty or has wrong settings?