Brian - I am getting this fault as well. I didn't get it on Mach 3 Turn, but I am getting it on Mill.
Using the same equipment (my lathe has a milling head) M3 M4 and M5 work perfectly on Turn, but when I ran off a program on Mill yesterday the line M3 S3000 was not accepted when running the program. The message "Unspecified error line ..." flashed up in a box, followed by a VB script window which was, I think, the M3 window with text DoSpin.
As soon as you close the VB window the program carries on.
I will have another look at it and see if I can be any more specific.
Jim