A new KB Article has been released for a SCOM agent or server with an error 623. One or more management servers and their managed devices are dimmed in the Operations Manager Console of Operations Manager 2007. The article can be found here: http://support.microsoft.com/Default.aspx?kbid=975057.
It deals with the Operations Manager Health service store running out of space as there are too many workflows running on the machine (agent or MS server). It gives the possibility to set it to a larger size through the registry.