I ran into this issue as well. - it was expanding a temporary file that was wound up being about 6 gigs too large to fit on my SSD. Here's what I did and plan to do in the future:

1) Short term I moved the game back to my larger HDD and patched it there where there is plenty of space. The end result is a 24.0 GB folder. I moved this back to my SSD, and all seems to be well with the world.

2) I moved the patch files (I have files going back to version 2.3 from the downloader) to the regular HDD; if I need to reinstall in the future, they're there.

3) I'm going to (probably) create a symlink between the Updates folder on the SSD and the regular HDD - this way, when it patches in the future, the patches get expanded on the HDD, where there is lots of space.

I won't know for sure if this works until the game comes back up live, but it seems to be a fix.