File not found error when opening a macro-enabled Excel file

I have an Excel file that I have been developing over many years and am distributing to 30+ customers on a regular basis. After the last update, 2 persons have reported a strange error. When trying to open the file by double-clicking it, they receive a "File not found" error before the file even opens.

I have not been able to reproduce the error on the few computers I've tried and several customers have reported back that they don't run into the problem.

Has anyone run into this behavior and know what to do about it?

Thanks in advance!