Upgraded to El Capitan OS X and now T-bird will not launch. Message: A copy of Thunderbird is already open. Only one copy of Thunderbird can be open at a time."
Yesterday I upgraded from Moutain Lion to El Capitan on my MacBook.
Previously Thunderbird worked fine. Now it will not launch and I get an error message that "A copy of Thunderbird is already open. Only one copy of Thunderbird can be open at a time." Unfortunately there is no other copies of Thunderbird running. If I look in the "Force Quit" window I don't see Thunderbird.
I tried deleting and re-installing Thunderbird with latest version. I still get the same message.
Firefox works fine. Can anyone help? Thanks!