[JavaScript Error: "Download request 1/PJBRN56S failed"]
[JavaScript Error: "Win error 5 during operation removeEmptyDir on file C:\Users\user\Zotero\storage\PJBRN56S (Access is denied.

You have to say what you're referring to, but if you mean this sync error, either a file that was deleted remotely is open on your computer, there's a permissions problem in your Zotero data directory, or security software on your computer is preventing Zotero from making changes to its data directory.