OK... use this code... remember to replace the username with your own...
This should remove all the special characters from your URL so it should work with twitter... please let me know.
Code:
<a href="http://twitter.com/share" class="twitter-share-button" data-count="horizontal" data-via="YOUR_TWITTER_USERNAME" data-url="{vb:raw vboptions.bburl}/showthread.php?t={vb:raw threadid}">Tweet</a><script type="text/javascript" src="http://platform.twitter.com/widgets.js"></script>