If you're running the Jasminum plugin, disable Jasminum, restart Zotero, and then reset translators from the Advanced → Files and Folders section of the Zotero settings.
If not, we'd want to see a Debug ID for reproducing this. (We never want raw error output here, just ids.)
If not, we'd want to see a Debug ID for reproducing this. (We never want raw error output here, just ids.)