After I had the Firefox update issue last month, I have the same issue with Thunderbird now!
The Thunderbird version installed is
After working with Robert on Mozilla bugs it seems this might be an issue if Mozilla products are installed in some location other than folder in Windows 7. I have installed Mozilla products in other folders
A point to note is even after changing permissions on the folder and running these products as Administrator I am unable to update.
Conclusion: Do not alter the default installation path of Mozilla products!