Well, I didn’t see this coming, mainly because I use the Beta builds as my default Thunderbird build on my desktop machine. I do run the Release version of Thunderbird on my laptop, but since I am on break from school, have not even turned on the laptop this week.
On December 23, 2011, Mozilla released an update for Thunderbird 9. Thunderbird 9.0.1, according to the (vague) release notes fixed an issue with Windows XP users not being able to run Thunderbird in some cases. Took a little hunting but this was related to Bug 712960. This is unrelated to the issues that caused there to be a chemspill release of Firefox 9.0.1 earlier this week as was the case with Firefox 8.0.0,8.0.1 the issues were isolated to Firefox only. User can update via Help > About Thunderbird or by manually downloading and installing Thunderbird 9.0.1 from the getthunderbird.com site.