Compatibility Excel 365 vs 2010

We have a workbook in which we work with several colleagues (sharing is off).
Now we will be migrating to office 365.
I already am on office 365.

The file was made by me in excel 2010 and I work most with it now also in excel 365.
It is a macro workbook.

The problem we now have is that when a colleague works in the workbook and tries to save they all get the similar error message :
"Errors were detected while saving......Microsoft excel may be able to save the file......etc".

Looked around on internet and already tried a few things with trust center settings but no luck.
Maybe someone of you had the same issue or just know what is going on and how to fix it?
Thanks.

lot of views but apparently nobody encoutered similar things?
Too bad.