How can second, third user sign excel file containing macro

Hi,

In our project we do not save file. Only sign. First user sign, but second,
third..user cannot sign. This works if file does not contain macro. But if
file contains macro, second, third,..user cannot sing. Gets the fallowing
message.

"This workbook must be saved as a Microsoft Office Excel Workbook before it
can be digitally signed. Saving will remove all existing signatures. Do you
want to save the workbook?"

If you test in your computer, you can see same warning.
How can second, third user sign excel file containing macro.

Thanks.