The dreaded 'Can't save here' for MS office files

Hello--I have a chronic problem with my file folders: frequently get 'Can't save here choose another location'.

I use my employer's MS Office 365 account, and sync Dropbox to Windows Explorer, and use Explorer for my file management.  The 'Can't save' message seems to appear when I am using many subfolders...if I go back one folder I can save the file.  The problem is, this doesn't work with my folder organizing system. Is there a limit to how many subfoldes can be used? If so, can I release that limit?  Or is the problem something else?

Thanks you!