As Dan mentioned we are in the process of changing which services you can connect your account to, but we don't expect any errors. I tried to connect another account to twitter, and didn't have any issues. Where were you trying to connect to twitter from (signup, or managing your account)? I'll look into this and see if I can find a problem.
I still don't see this error you're getting. Are you still having this issue? Do you get the error once you click the 'Connect' button, or after you fill in your Twitter account details? Anything else you can tell us will help. Thanks!
I found the source of this problem. It is a bug on our side preventing certain users from connecting to Twitter. However, we will shortly be removing the ability for all users to connect to Twitter, so we will not be fixing this.