Sync offline changes with online sheet

I have a sheet that I make changes to offline and need to sync with the online copy. When I open my offline copy in Excel I then login to Zoho with the add-in. If I use the add-in save feature it tells me that the file does not exist online, even though it is the same file with the same file name. I can upload another copy, but it is shared so I don't want to have to continue to re-invite viewers. Any suggestions? Thanks and great product!