To fix Ada tasking in FreeBSD 9.0, you have to fix and rebuild the thread library.
Before you start, make sure you have the FreeBSD 9.0 source at /usr/src. If you didn't install it with FreeBSD, you can find src.txz on the install disk. Alternatively, you can download the 89MB file directly from FreeBSD Just extract it in the root directory as it starts with /usr.
Now Ada tasking should function correctly on FreeBSD 9.0. This has already been fixed for the upcoming FreeBSD 9.1.