ERROR: syscache lookup for index 245488730 failed

Hi,

I've found this message in my server log:
ERROR:  syscache lookup for index 245488730 failed

What is cause of this error and how can I avoid it?

I think that this is caused by issuing commands like "reindex table xxx;"
from cron and simoultaneously running pl/pgsql functions using these
indexes. But this error occures only sometimes. How can I do regular
reindex safely?

I was thinking about wrapping the reindex command and recreation of
pl/pgsql functions in a transaction but it's not possible...

This is on 7.2.

Thanks               kuba