Comment 63 for bug 996245

Serial starts wiht 121xxxxxxxxxxxx , looks like your's is old model that needs HW modification.
I'm not 100% sure but my 1st with 121 was windows only board.

There was some guy at mac forums that had picture what solder to older boards to fix it (per request of gigabyte support), it was removed tho so can't say if it was legit.