Unhandled command '911' indicates some form of authentication error.
This could be simply that your password is wrong.

Other reports of this error seem to indicate that it could be a timeout
problem, if the authenticaion process takes too long to complete, the
authentication fails.
Slowness could be caused by a number of factors, including:
 - being on dialup
 - slow DNS resolution
 - network problems.

Please check that your configured DNS servers are correct, and are resolving
hostnames reasonably quickly. On Linux these are specified in
/etc/resolv.conf - At least 5 people resolved the '911' error by removing
incorrect DNS servers from here.

If you are still having problems please try these tests to try to identify
any potential network problems:
using telnet, try connecting to
 - port 1863 on messenger.hotmail.com
 - port 443 on loginnet.passport.com
 - port 443 on login.passport.com
If any of those fail, or take a long time to connect, then this is probably
not a Gaim bug.