Zotero recommends:
1. Make sure you are running the latest version. To see what version you're running, On a Mac, select "About Zotero" from the Zotero menu. With Windows or Linux, select "About Zotero" from the help menu. Upgrade Zotero if you are not running the latest version.
2. Check Zotero's troubleshooting pages.
3. Search the Zotero forums. See if someone else has encountered the problem--and if it has been resolved.
4. Post to the forums. Before doing so, you must create an account, read the forum guidelines, and review the procedures for reporting problems. Find here documentation for how Zotero support works.