I'm on a Mac with El Capitan and am running the latest version of Mist.It's stuck on block 1,150,006 and I'm not sure why neither do I know what to do...
1) Double Check Mist Version
You are on an outdated version of mist. Upgrade to 0.5.2 or later.
There was a hard fork on block 1,150,000 - referred to as the homestead release. Read more on this:
2) Reset the blockchain
If you are on the latest version of mist but still stuck, reset your blockchain.
Find your ethereum blockchain files. You are usually using
geth which was included with the mist release. Try removing:
And start mist again. Now you will have to resync the whole chain but it should not get stuck at the Homestead fork. (1,150,006 is the latest Frontier block by the way.)