One good way of Authenticating against CRM Webservice is not tell CRM which internally defined system user account you wish to authenticate against. I found this good article from Microsoft about how to lookup the system user account based on the GUID that it receives in CRM after you have told CRM that you wish [...]
While working in a project where we integrate with CRM, I noticed how important it is not to mix the ways you can integrate with.
Either you create a reference to the CRM Web service in your Visual Studio project and the proxy classes are generated.
Or you can reference microsoft.crm.sdk.dll and microsoft.crm.sdktypeproxy.dll that exists in the CRM [...]
