Try this first, normally works for me (from Mojo site)
The lockout on my fork does not work, what do I do? (Open bath forks only)
A. It may be that the cartridge needs bleeding. For instance, if the bike has been stored upside down or the fork has not been used for a while.Try this proceedure below before sending your fork to us.
With the lockout off, turn the rebound to full slow (fully closed)
Push the fork up and down slowly 2 or 3 times.
Now bring the rebound adjuster back 3 clicks and push the fork up and down another 2 or 3 times.
Now try your lockout, it should be working fine.
PLEASE NOTE: If you have RLC or RLT versions, make sure your threshold adjuster (located at the bottom of the fork leg) has been turned to the firmest setting.