Cache lookup?

I've installed postgres 6.5.2 on Red Hat Linux 6.1 (kernel 2.2.12).
Whenever I try a "\d" in psql, I get the following error:

ERROR: cache lookup for userid 101 failed

User 101 is postgres. This doesn't happen when I install postgres from the
RPM's. I can't find this anywhere, and looking at the code doesn't help all
that much, either...

RPM's are great, but if we ever move to Caldera's distribution (which looks
more likely since Netfinity is looking good), I'll need to compile to
install, just like this.

Thanks,
Neil