Standalone detecting open copy of Zotero when none is running
I'm new to Zotero, using it on a Mac. Through a series of mishaps trying to backup my data, I've clearly screwed something up. Besides wiping out my initial data (not much, so no big deal), I can no longer start Standalone. I get the following message: "A copy of Zotero is already open. Only one copy of Zotero can be open at a time." No other copy of Zotero is running -- Firefox is shut down. I've tried uninstalling both the Standalone and the Firefix add-ons (twice) and I still get the message. Any help anyone can provide would be great.
Anyone from Zotero care to chime in? :)
TIA
Thanks Simon!
Because of this problem I restarted the mac more than three times today and none of them were proper restarts, I had to manually shut down by holding the power button.
So please, any other suggesstions?