In CRM 4.0 the MS CRM Workflow Service is not available anymore. CRM 4.0 has one Async Service the 'Microsoft CRM Asynchronous Processing Service'. The Microsoft CRM Asynchronous Processing Service takes care of all asynchronous processess that run within CRM like Workflow and Plugins (former Callouts).
The Microsoft Dynamics CRM system architecture can be divided into 3 major components: the core system, which features the event execution pipeline, the database component, which hosts the asynchronous queue, and the asynchronous service. One benefit of the scalable architecture of Microsoft Dynamics CRM is that the asynchronous service can be hosted on servers other than the Microsoft Dynamics CRM server. This distributed processing capability can result in improved performance of Microsoft Dynamics CRM.
At a client I work on a CRM 4.0 system, my help was asked when updated workflows (from CRM 3.0 to CRM 4.0) that worked in CRM 3.0 did not work.
I soon came to the conclusion that the workflows did not even started. First I tried changing the executing identity on the service, which did not change anything.
After googling I found that lots of people had this problem and that the problem always was related to the MS CRM Website running with a hostheader, or second ip-address.
After trying out several different options my conclusion is that:
CRM 4.0 needs to run without a hostheader and with the IP-address option 'All unassigned' chosen.
So you cannot use another IP-address and you cannot use hostheaders (if you want the workflow to function)!
I already found out that the CrmDiscoveryService Web service under the hood uses the machinename to connect to the CRMService and the MetadataService, when I tried to register a Plugin using the PluginRegistration Tool.
Which in itself is remarkable IMHO, the reason for a DiscoveryService is, I think, to decouple these services, which is rather hard if you can only connect using the machinename.
Anyway, if you got this issue make sure you use the following settings (the TCP port is not important in this case, you can use 5555 or 80 or another port):
All unassigned without hostheader
My thoughts exactly...