I just helped someone that was having this problem in Excel when opening multiple spreadsheets from the network. this is the error she was getting:
the problem is that she had created some shortcuts to the network drives, and thus increasing the length of the path to such files. according to Microsoft only 218 characters are allowed on file path lengths ( that includes that path and the file name, this seems primitive to me ) and that’s why such error is displayed.
the solution is to use a network drive ( if you have the permissions to create one ) to shorten the path to the files so the file path length is shorter than the 218 characters Microsoft allows.
I hope that help someone.