Unable to update OptionSetValue field on CRM 2011 custom Entity - dynamics-crm-2011

Question

I'm getting a "Specified cast is not valid." Exception when trying to update an OptionSetValue attribute of a custom field on a custom entity.
This works:
data = new Xrm.Xyz_data()
{
Xyz_dataId = (Guid)entity["xyz_dataId"],
// Xyz_dataStatus = new OptionSetValue(5),
Xyz_IsSyncReqd = true
};
service.Update(data);
But uncomment the OptionSetValue line and it throws this exception:
System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]: Specified cast is not valid. (Fault Detail is equal to Microsoft.Xrm.Sdk.OrganizationServiceFault).
With this stack trace:
Server stack trace:
at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
Exception rethrown at [0]:
at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
at Microsoft.Xrm.Sdk.IOrganizationService.Update(Entity entity)
at Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.UpdateCore(Entity entity)
at Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.Update(Entity entity)

Answer 1

That looks right to me - I don't use early bound which it looks like you are doing but can you verify that the data context has been refreshed since the picklist attribute was created and published?
If this is a built in state field you will probably need to first do the update and then perform a UpdateStateValueRequest. Excerpt from CRM 2011 SDK -
#region How to update state value
// Modify the state value label from Active to Open.
// Create the request.
UpdateStateValueRequest updateStateValue = new UpdateStateValueRequest
{
AttributeLogicalName = "statecode",
EntityLogicalName = Contact.EntityLogicalName,
Value = 1,
Label = new Label("Open", _languageCode)
};
// Execute the request.
_serviceProxy.Execute(updateStateValue);
#endregion How to update state value

Answer 2

So I finally figured out what was happening. I turned on server side debugging using the same registry settings as CRM 4.0:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSCRM]
"TraceEnabled"=dword:00000001
"TraceCategories"="*:Error"
"TraceCallStack"=dword:00000001
"TraceRefresh"=dword:00000001
I reran my test that was failing, and found this error:
[2011-10-24 18:19:37.990] Process: w3wp |Organization:00000000-0000-0000-0000-000000000000 |Thread: 14 |Category: Platform |User: 00000000-0000-0000-0000-000000000000 |Level: Error | ExceptionConverter.ConvertMessageAndErrorCode
at ExceptionConverter.ConvertMessageAndErrorCode(Exception exception, Int32& errorCode)
at ExceptionConverter.ToSingleFaultOther(Exception exception)
at ExceptionConverter.ToSingleFaultUntyped(Exception exception)
at ExceptionConverter.ConvertToFault(Exception exception)
at ExceptionConverter.TryConvertToFaultExceptionInternal(Exception exception, Boolean createNewFaultException, FaultException`1& faultException)
at FaultHelper.ConvertToFault(Exception exception)
at OrganizationSdkServiceInternal.Update(Entity entity, CorrelationToken correlationToken, CallerOriginToken callerOriginToken, WebServiceType serviceType)
at
at SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs)
at DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc)
at ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc)
at ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc)
at MessageRpc.Process(Boolean isOperationContextSet)
at ChannelHandler.DispatchAndReleasePump(RequestContext request, Boolean cleanThread, OperationContext currentOperationContext)
at ChannelHandler.HandleRequest(RequestContext request, OperationContext currentOperationContext)
at ChannelHandler.AsyncMessagePump(IAsyncResult result)
at AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
at AsyncResult.Complete(Boolean completedSynchronously)
at ReceiveItemAndVerifySecurityAsyncResult`2.InnerTryReceiveCompletedCallback(IAsyncResult result)
at AsyncThunk.UnhandledExceptionFrame(IAsyncResult result)
at AsyncResult.Complete(Boolean completedSynchronously)
at AsyncQueueReader.Set(Item item)
at InputQueue`1.Dispatch()
at ScheduledOverlapped.IOCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
at IOCompletionThunk.UnhandledExceptionFrame(UInt32 error, UInt32 bytesRead, NativeOverlapped* nativeOverlapped)
at _IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)
>System.InvalidCastException: Microsoft Dynamics CRM has experienced an error. Reference number for administrators or support: #9F125FAE: System.InvalidCastException: Specified cast is not valid.
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyEntry.IntentionalRethrow(Exception chainException, Exception originalException)
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyEntry.RethrowRecommended(Exception chainException, Exception originalException)
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyEntry.Handle(Exception exceptionToHandle)
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicyImpl.HandleException(Exception exceptionToHandle)
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicy.HandleException(Exception exceptionToHandle, String policyName, ExceptionPolicyFactory policyFactory)
> at Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.ExceptionPolicy.HandleException(Exception exceptionToHandle, String policyName)
> at Common.Services.ExceptionPolicy.HandleException(Exception exceptionToHandle, String policyName)
> at XYZ.CRM.Common.Services.ExceptionPolicy.HandleException(Exception exceptionToHandle, String policyName)
> at XYZ.CRM.Plugin.Common.PluginBase.OnError(Exception ex)
> at XYZ.CRM.Plugin.Common.PluginBase.Execute(IServiceProvider serviceProvider)
> at Microsoft.Crm.Extensibility.V5PluginProxyStep.ExecuteInternal(PipelineExecutionContext context)
> at Microsoft.Crm.Extensibility.VersionedPluginProxyStepBase.Execute(PipelineExecutionContext context)
And since I was debugging my plugin via a unit test, I realized that another plugin was getting fired when those fields were updated by my plugin, and that plugin was apparently causing an exception. But even worse was that the exception handler was causing another exception, that was getting returned, masking the true exception. I tested a really simple fix by eating any exceptions that the exception handler might throw, and it is working great now! Now to discover why my other plugin is failing...