Jordan Windsor posted on Wed, 27 Jun 2012 13:16:44 +0930 as excerpted:

My computer locked up and I had to press the reset button.
Ever since then I can't mount the btrfs filesystem, here's the output:

Are you aware of the btrfs wiki and have you read up on btrfs there, yet?

https://btrfs.wiki.kernel.org/index.php/Main_Page

In particular, check the mount options listed there.  I had a similar 
problem when I was testing here (during the 3.4 kernel dev cycle, I 
decided btrfs was still too experimental for my current needs so am back 
on more reliable reiserfs for now), which turned out to be a corrupted 
space-cache.  Mounting with the listed nospace_cache option allowed the 
filesystem to mount and self-repair, after which I could mount it 
normally again.

https://btrfs.wiki.kernel.org/index.php/Mount_options

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman