pkgdb problem after portupgrade - operation not permitted

[Max Belushkin]

I just portupgrade'd portupgrade on a FreeBSD 6.0-RELEASE to portupgrade 
2.0.1 (2006/06/18), and right after this pkgdb fails on all operations, 
i.e.:
pkgdb -fu
[Rebuilding the pkgdb <format:bdb1_btree> in /var/db/pkg ... - 63 
packages found (-0 +63)
Operation not permitted: skipping...
.
Operation not permitted: skipping...
.
... etc.
Operation not permitted: Cannot update the pkgdb!]

Naturally, portupgrade itself now fails to do anything. I've googled for 
  the "Operation not permitted" error in pkgdb, but I could not find any 
useful pointers to the source of the problem. Any help is much appreciated.