I have same problem it is driving me nuts. My current workaround is to save the file to my desktop so I don't lose work. Then I manually copy the file to the relevant One Drive folder using Windows Explorer. Then I open the file by double-clicking open it. Sometimes it's fine, other times it tells me there are problems saving. In which case I close the Microsoft Office application and then reopen it. Occasionally I need to reboot the PC and resync one Drive.
Sometimes when I get the error and I hit enter a few times and it saves ok. From my guesstimate it's a bug with the syncing of One Drive. So much for the cloud revolution...