I don't suppose it helps if you open the Excel sheet in a browser
window instead of in Excel?

This produces another error where the browser will continuously try to save
the file (and produces nasty error messages on every click). Our dealers
have therefore been advised to first download the file and then use it.
For info: the file is a "Marketing Planner" the dealers should also use for
their own planning in dependance of the manufacturer's activities.

Thanks for the hint anyway.

Regards

Michael