I am getting plenty of work on both mine, and I have a card that is similar to yours.
My driver is newer. I always get the driver from ATI and not the computer manufactures website or a Microsoft update. I remember there was some other issue a while back, but I do not remember what it was. Most of the time lately it has been someone changing the Global venue, but then the computer is under another venue (School, Work, Home), so even though it looks like it's requesting, the options are not allowing it.
My lucky numbers are 121*2^4553899-1 and 3756801695685*2^666669±1