Steam failed to load 0xbfffe078 and error 1 occurred

Hello there,
When I opened my MAC today and started the Steam I got this error which it says that another steam is opened. I have verified all the programs that are open and I didn’t find any other steam opened. I have rebooted the MAC and the error appeared again. Can anyone help me to start the steam on my MAC ?
Thanks !

Steam failed to load: *steamstartEngine(0xbfffe078) failed with error 1: A Steam Engine Instance already exists
OK
