Fatal error 'Spinlock called when not threaded.'

[John Abrams]

After cvsup-ing I get "Fatal error 'Spinlock called when not
threaded.' at line 87 in file
/usr/src/lib/libpthread/thread/thr_spinlock.c (errno = 2)" when I try
portupgrade, portversion or pkgdb.

How can I fix this error?

This is a FreeBSD 5.5-STABLE system.

-ja