This comes directly from the Ubertwitter site
Source 7 August - Continued Twitter Service Issues
The Twitter service and in particular Twitter's interface which third party clients like ÜberTwitter use to talk to Twitter is still experiencing slowness and occasional timeouts. Until Twitter can resolve the issue you will continue to experience problems retrieving timelines and posting tweets using ÜberTwitter and any other clients.
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CodeWarden There have been numerous threads exactly like this one that have popped up in the past 24 hours. All of them with the same responses.
Twitter was hacked. There is nothing anyone can do to help fix the problems you are having. It will be like this until Twitter fixes their API.