WebNotifications set up - "An unexpected error occurred"

[chrismarkovic]

Hello everyone!
When attempting to set up the portal with an on-premise environment, I have encountered some issues with Cache invalidation. i have confirmed that the URL for Cache invalidation is correct and both resolvable from the CRM server and receives and "OK" as expected, but following the set up of the Notification URLs, rather than the double list for entity selection I receive an error instead

I have attempted with different browsers, checked the application logs on the CRM system and also checked the plugin trace on the page load. There are no exceptions or information of note in the plugin trace.

the application log reports the following:

------ Begin
Provider
[ Name] MSCRMWebService

• EventID 18176
  [ Qualifiers] 49152

d123b611-2d9e-e011-b649-5e63b2137187
0be4fe20-6cad-4b33-8dcd-118352d18559
none
30
RetrieveMetadataChanges
Microsoft.Crm.Extensibility.InternalOperationPlugin, Microsoft.Crm.ObjectModel, Version=8.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
Microsoft.Crm.Extensibility.InternalOperationPlugin
Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor) at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Web.Services.Protocols.LogicalMethodInfo.Invoke(Object target, Object[] values) at Microsoft.Crm.Extensibility.InternalOperationPlugin.Execute(IServiceProvider serviceProvider) at Microsoft.Crm.Extensibility.V5PluginProxyStep.ExecuteInternal(PipelineExecutionContext context) at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context) Inner Exception: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.Crm.ServerLocatorService.GetDeploymentSetting[T](String settingName, T defaultIfNotFound) at Microsoft.Crm.Metadata.Query.SelectFromMetadataCacheStrategy.get_MaxDepthOfNestedFilters() at Microsoft.Crm.Metadata.Query.SelectFromMetadataCacheStrategy.ValidateConditionAndFilterNesting(String metadataEntityName, MetadataFilterExpression filter) at Microsoft.Crm.Metadata.Query.SelectFromMetadataCacheStrategy.GetFilterExpression[TSource,TDestination](String metadataEntityName, MetadataFilterExpression filters) at Microsoft.Crm.Metadata.Query.SelectFromMetadataCacheStrategy.SetMetadataFilters(String metadataEntityName, MetadataFilterExpression filters) at Microsoft.Crm.Metadata.Query.MetadataQuerySelectVisitor.UpdateStrategyWithQuery(String metadataEntityName, MetadataQueryExpression query) at Microsoft.Crm.Metadata.Query.MetadataQuerySelectVisitor.Visit(EntityQueryExpression query) at Microsoft.Crm.Sdk.Metadata.MetadataServiceProvider.RetrieveMetadataChanges(EntityQueryExpression queryExpression, Nullable`1 filters, String clientVersionStamp, ExecutionContext context, String& serverVersionStamp, DeletedMetadataCollection& deletedMetadata)

---- end

there are also no errors in the CRM IIS logs. All seems normal.

Has anyone ever encountered this before?