If you're running XP you can try deleting this file:
C:\Documents and Settings\All Users\Application Data\Malwarebytes\Malwarebytes' Anti-Malware\
rules.refAnd attempt the rules update download again.
If that does not work then it's also quite possible that either your Anti-Virus is blocking the update, program or you may be infected.
Please see the
FAQ if your Anti-Virus is possibly blocking otherwise you may need to have someone assist you with Malware detection and removal.
We don't work on Malware removal in the general forums.
Please print out, read and follow the
directions here, skipping any steps you are unable to complete. Then post a
NEW topic here.
One of the expert helpers there will give you one-on-one assistance when one becomes available.
After posting your new post make sure under options that you select
Track this topic and choose one of the Email options so that you're alerted when someon has replied to your post.
Alternatively, as a paying customer, you can contact the help desk at
support@malwarebytes.org