hi guys,
i am sure that if you are using Hummingbird you have realised you cannot follow or unfollow anyone. This is because a recent Twitter update has had a negative impact on this tool and the API usage.
i reckon un patch will be produce soon (at least i'd like to hope), in the meatime you can unfollow and follow using other tools such as:
http://www.tweepular.com
http://www.huitter.com/mutuality/
http://dossy.org/twitter/karma/
again, use them at your own risk...