Sharepoint 2010 Visio Workflow Visualization Error

I was faced with the following error when I tried to enable workflow visualization on SharePoint 2010

System.OperationCanceledException: The server failed to process the request. ---> System.ServiceModel.ServerTooBusyException: The HTTP service located at http://r9k7y7d:32843/80eb32d02df348f595a9d27e97f7238c/VisioGraphicsService.svc is too busy.  ---> System.Net.WebException: The remote server returned an error: (503) Server Unavailable.
   at System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult)
   at System.ServiceModel.Channels.HttpChannelFactory.HttpRequestChannel.HttpChannelAsyncRequest.CompleteGetResponse(IAsyncResult result)
   --- End of inner exception stack trace ---

Server stack trace: 
   at System.ServiceModel.AsyncResult.End[TAsyncResult](IAsyncResult result)
   at System.ServiceModel.Channels.ServiceChannel.SendAsyncResult.End(SendAsyncResult result)
   at System.ServiceModel.Channels.ServiceChannel.EndCall(String action, Object[] outs, IAsyncResult result)
   at System.ServiceModel.Channels.ServiceChannelProxy.InvokeEndService(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.Office.Visio.Server.GraphicsServer.IVisioGraphicsService.EndGetVectorDiagram(IAsyncResult asyncResult)
   at Microsoft.Office.Visio.Server.Administration.VisioGraphicsServiceApplicationProxy.GetVectorDiagram(VectorDiagramRequestContract vectorDiagramRequest)
   at Microsoft.Office.Visio.Server.ServiceWrapper.GetVectorDiagram(String visioFileUrl, Int32 pageNumber, Boolean disableRefresh, AddonDataSource[] dataSources)
   --- End of inner exception stack trace ---
   at Microsoft.Office.Visio.Server.ServiceWrapper.GetVectorDiagram(String visioFileUrl, Int32 pageNumber, Boolean disableRefresh, AddonDataSource[] dataSources)
   at Microsoft.Office.Visio.Server.GetDiagramAsyncTask.GetVectorDiagram()

After some tinkering and scratching my head, these are the steps I took which made it work!

1. First follow the steps here: http://technet.microsoft.com/en-us/library/ee524058.aspx
2. Create an apppool that uses LocalSystem.
3. What I did at first was to use the wrong app pool for my service. When I changed the AppPool to the one with Identity: LocalSystem, it worked!