Add known troubleshooting case for Pull Server

where the certificate common name is different than the DNS name.  
fyi @Austinm2559

dsc/troubleshooting/troubleshooting.md

@@ -707,6 +707,23 @@ onlyProperty                            PSComputerName
 14                                      localhost
 ```
 
+## DSC returns "unexpected response code InternalServerError" when registering with Windows Pull Server
+
+When applying a metaconfiguration to a server to register it with an instance of Windows Pull Server,
+you might encounter the following error.
+
+```PowerShell
+Registration of the Dsc Agent with the server https://<serverfqdn>:8080/PSDSCPullServer.svc failed. The underlying error is: The attempt to register Dsc Agent with AgentId <ID> with the server 
+https://<serverfqdn>:8080/PSDSCPullServer.svc/Nodes(AgentId='<ID>') returned unexpected response code InternalServerError. .
+    + CategoryInfo          : InvalidResult: (root/Microsoft/...gurationManager:String) [], CimException
+    + FullyQualifiedErrorId : RegisterDscAgentUnsuccessful,Microsoft.PowerShell.DesiredStateConfiguration.Commands.RegisterDscAgentCommand
+    + PSComputerName        : <computername>
+```
+
+This can occur when the certificate used on the server to encrypt traffic has a common name (CN)
+that is different than the DNS name used by the node to resolve the URL.
+Update the Windows Pull Server instance to use a certificate with a corrected name.
+
 ## See Also
 
 ### Concepts