1. Check that the Twitter plugin is installed and enabled (Global settings > Plugins > Twitter plugin)
2. Check that outgoing pings are enabled (Global settings > Features > Outbound pings > Immediate)
3. Link your twitter account either on User profile page (for posts made by you) or Blog settings > Plugin settings (for any post in the blog)
4. Enable Twitter pings (Blog settings > Advanced > Ping twitter.com)
How to send new posts to my Twitter account
1. Check that the Twitter plugin is installed and enabled (Global settings > Plugins > Twitter plugin)
2. Check that outgoing pings are enabled (Global settings > Features > Outbound pings > Immediate)
3. Link your twitter account either on User profile page (for posts made by you) or Blog settings > Plugin settings (for any post in the blog)
4. Enable Twitter pings (Blog settings > Advanced > Ping twitter.com)
ps. I kinda like friendly b2evolution GUI ;)