Portupgrade fails after buildworld

[Attos]

Hi,
I'm sure this has been discussed before but I haven't find the source.
I recently upgraded a machine from 5.4 to 6.0. Everything went OK
until I cvsup'ed the ports collection and ran portupgrade. Some of the
ports failed. I recall that this is a problem related to the ports
collection and the kernel being out of sync. How do I fix it?
--
Attos Janus