Take a look at the error message. It tells you that a particular file can't be created, likely because of an invalid character in the filename. Assuming that's from another computer of yours (rather than from a group), rename that file on the other computer, relink it in Zotero (if you renamed it from outside of Zotero), and sync it again.
This shouldn't happen, of course, so if you can let us know how you saved that file (e.g., via import, from a particular site via the URL bar icon) we'll see if we can prevent this in the future.
Upgrade Storage
This shouldn't happen, of course, so if you can let us know how you saved that file (e.g., via import, from a particular site via the URL bar icon) we'll see if we can prevent this in the future.