OK - if you have this installed - one query may fail when you run the 6.4 altertable. As w already have the U_BirthDay field - the query in 6.4 which adds U_Birthday conflicted on my tests.
Backup your database first! I developed this for my own needs so use at your own risk. The attached file - download it and raname it from .txt to .php. Upload it to your ubbthreads directory.
Then AFTER you run your 6.4 altertable, run the convertbday.php script.
It will change the name of the old birtday field.... add the new fields (which may have failed with the 6.4 altertable) and convert all the previously entered birthdays with this mod to the new UBB.Threads version 6.4 birthday field.
After be sure to remove it from your server!