WCF Impersonation Level Error on System.Data.OracleClient - wcf

Question

I currently have a WCF service running in IIS7 and I have have added impersonation on each of the public web methods with the following:
[OperationBehavior(Impersonation = ImpersonationOption.Required)]
public void TestMethod(){}
When ever I call this method from my test client application I get the following error:
Could not load file or assembly 'System.Data.OracleClient, Version=4.0.0.0, Culture=neutral, PublicKeyToken=waeraewrar' or one of its dependencies. Either a required impersonation level was not provided, or the provided impersonation level is invalid.
I'm currently using Microsoft Enterprise Library 3.1, and .Net 4.0.
Sample code:
WcfService client = new WcfService();
client.TestMethod();

Answer 1

Try configuring the client to allow an impersonation level of impersonation. For example:
<system.serviceModel>
<client>
<endpoint address="http://xxxxx/Services/xxService.svc"
binding="wsHttpBinding"
contract="IServiceContract"
behaviorConfiguration = "ImpersonationBehavior" />
</client>
<behaviors>
<endpointBehaviors>
<behavior name="ImpersonationBehavior">
<clientCredentials>
<windows allowedImpersonationLevel = "Impersonation" />
</clientCredentials>
</behavior>
<endpointBehaviors>
</behaviors>
</system.serviceModel>
See this article for more on impersonation and delegation.

Answer 2

The error message suggests that the problem is that the impersonating user doesn't have access to the System.Data.OracleClient assembly DLL in the file system, and thus can't load it.
Can you not cause the System.Data.OracleClient assembly to be first loaded by code outside the service methods requiring impersonation... i.e. by code running with the IIS worker process identity. For example in your service instance constructor.
Once the assembly is loaded into the service's AppDomain, the service methods running under impersonation shouldn't need to do so again.