This is an obvious one but I thought it worth mentioning as amongst other issues this held me up on a client site yesterday. The client has wrapped the BizTalk rules framework in a web service that exposes specific policies. Various components including windows services call the rules engine service. One of those windows services was throwing an error when it hit the rules service, even though I could browse to that service. So I double checked the certificates being used, the IIS config, the SQL instance, and the security on the rules engine database. All looked good.
Anyhow, to cut a long story short the Rules Engine Update service had stopped and I hadn’t noticed. No failed service notifications on reboot and I didn’t notice anything in the event logs amongst the thousands of other information event logs logged on reboot. Talk about event log polution!
When using the rules framework the policy class is fetched from a cache stored in memory and maintained by the rules engine update service. It’s always the obvious things!!! Mental note, if calls to the rules engine are failing check REU first.