I'm curious on this... seems very strange.

Simon, if you can describe what you do to replicate the issue, step by step, and the exact verbiage, that would be great.

Also, go into the VBE for the workbook, and see if you have anything in a References folder for the project. Check range A100 to see what it says as well.

If you can't find anything, could you email me a copy of your workbook? I'll PM you my email address.

Cheers!