Can’t upload - we can’t merge your changes with those made by someone else

TimothyBult 

I get that message, but only occasionally (not frequently, as you indicate is your experience). My files are all stored in OneDrive. I do go back and forth between a MacBook Air and a desktop iMac, and that use of multiple devices is no doubt a part of what's happening. In fact, it probably IS the underlying cause. I suspect it can be a case where the synchronization with the file-in-the-cloud hasn't happened (for whatever reason that can be).

In the one file that is most frequently involved, a spreadsheet I use to track investments, Excel always give the option to discard changes or save a copy. I choose one or the other, depending on how much I've just done.....and then complete the comparison and update on my own.

I'm not helping resolve your case, I'm sure....just letting you know you're not alone. I don't think the issue is in Word or Excel, however. It's in the syncing (or lack thereof).