That is a very old version of mojoPortal, it used the version 1 of the twitter widget. About 10 months ago we updated to the newer version 2 widget. My guess is that twitter has now discontinued the old widget if it no longer works.
I'd recommend upgrading but since it is a very old version you should definitely backup all the site files and the database, and read the upgrade guide and review all the release notes in the blog for versions since your current version as well as the important skin changes article before upgrading. Also make sure you are using MS SQL 2005 or higher since we dropped support for MS SQL 2000 back in version 184.108.40.206.
Alternatively if you don't want to upgrade you could remove the twitter widget and use an html content instance and just embed the latest widget code generated by twitter.
Hope that helps,