Hi, Thank you for the quick response. Unfortunately the file is commercially sensitive so I cant send in a completed form. I might be able to strip out the single element.

I have used the onkey command many times, in many excel tools that I have developed, but I have not seen excel do this before!! The work computers have recently been upgraded to Win7 and Bit locker, which does from time to time have strange affects.

Is there any common or known reason, for the behaviour, where excel tries to call the function in a new copy of the same file?