As some of you may have noticed, the Twitterbot seems to always fail to authenticate properly against twitter's basic HTTP authentication prompt when run from Mono 1.2.3 on Mac OS X. This was neither an error in twitter's webservice (I have been running my bots from a FreeBSD machine with Mono 1.1.13 for some time now) nor in the Twitterbot code itself, but rather a regression in the System.Net.Configuration namespace, I'll let "kangaroo" (the developer who found and fixed the bug) explain:

13:03 <@kangaroo> ok its falling in to DoPreAuth
13:04 <@kangaroo> Authorization auth = AuthenticationManager.PreAuthenticate (this, creds);
13:04 <@kangaroo> thats returning null
14:04 <@kangaroo> got a patch for you
14:04 < rtyler> to compile into mono or my app?
14:05 <@kangaroo> http://monoport.com/1821
14:05 <@kangaroo> mono
14:05 <@kangaroo> you need a new System.dll

The patch should make it into the next bug-fix release of Mono (1.2.3.2) and should allow you to once again run Twitterbot on Mac OS X, otherwise you might want to try another machine, or step back a few point releases if it's that critical to have you Twitterbot running.