The latest DHCP Management Pack release (version 05.0.3500.0000, released 10/27) for MOM 2005 SP1 has an issue when imported on a management server where no previous version of the MP exists.
When one of the State alerts ('The DHCP Scope is running low or out of available Addresses' or 'The DHCP Superscope is running low or out of available Addresses') is generated by the MP you will receive an alert stating Invalid Role 'DHCP' in Rule 'The DHCP Scope is running low or out of available Addresses'. If the event rule properties are examined the Alert tab will display no properties for Server Role, Instance or Computer.
This issue should affect only new installations of the DHCP and not those upgrading from the previous version.
We are working on re-releasing an updated version of the DHCP MP and I will post an update nearer the release.
Clive Eastwood (Supportability Program Manager - System Center Operations Manager)