This problem could be related to the Twitter worm that surfaced over the last weekend but Twitter has deleted all tweets from my account that were written during the last three days.
Deleted Tweets can be recovered
Luckily, the permalinks of all deleted tweets are still valid so any links pointing to your Twitter updates won’t break. For instance, this sample tweet is erased from my profile but it continues to exist as before on Twitter.
Update: Looks like I am not the only one affected due to this mass but silent clean-up happening at Twitter. They should have at least informed us beforehand.