I've had this error several times. I believe its some kind of delayed communication error with the COM port between the PC and the CMM Controller. Why it happens, I don't know.
I do have a Visual Basic App that run's in my CMM Part Program and when I incorporated this VB App, That's when I started getting this error. The VB App gets Executed via the "GI,WINEXE" CMES command so I don't know if that command is the cause.
I've had the error come up maybe 5 - 8 times total out of 100.
In most cases, when I get the error, I just hit the OK button and my program continues running. Strangely, it only happens to one particular part program. All my other part programs never had the problem.
I only run my programs in WINCMES.