I solved this issue for me.
I suspect the problem lies in the way Yosemite handles partitions and formatting of drives.
Anyway, what I did was:
Put the SSD into my BlackMagic Cinema Camera and formatted it in the EXFAT option (which evidently also deleted all partitions and created a single one).
Put the disk back into my macbook and booted from the firmware updater CD.
And it suddenly worked.
If you don’t have said camera (and I assume most people on this thread don’t),
you might still have windows machine that would allow you to do the same thing, or try and format it that format on the mac.
I suspect, however, you’d also need to remove all other partitions (mac recovery partition etc), for this to work.
A clean Yosemite install may also have used the new partition scheme, which DiskUtil can’t change. This is something you can revert to the old thing though (google search it).
Anyway, it was a major headache.
If you’re going to do any of the above, make sure you have a current TM backup.
