E2k3 PF hierarchy or content not replicating in or out of a particular server. Using Sophos Pure Message?

We've had a couple of cases where Subject tagging in the product has caused PFs to stop moving out the server.

The way we found this was quite typical for a PF case...

Use diagnostic logging on the server in question for PF and the IS objects

Find the message in the events logged

Track the message and found it only gets as far as the Categorizer.

This led me to some previous cases where PureMessage can cause this if subject tagging is on

Hope that helps somone!