SharePoint custom approval workflow end with "Error Occurred"

Hi,

I have 2010 VS custom approval workflow.

All my items got approved by users which is handled in aspx.cs file button click and on ListItemUpdated we have workflow which will check all the task related to this item and update the request status as Approved/Rejected.

My issue:

All my task are approved by users but before updating the request status, in workflow i am getting below errors and workflow status shown as "Error Occurred". Custom error handling in workflow also not logged with our method specific details so not sure where the error happening.

The main concern here is this is not happening regulalry. this happen only once or twice in a month out of 100+ request items.

Can any one help me?

Below is Workflow History:

8/22/2013 9:58 PM

Error

System Account

An error has occurred in eXXXWorkflow

ULS Log:

08/22/2013 21:58:36.35* w3wp.exe (0x10D4)                        0x1338 SharePoint Foundation         Workflow Infrastructure        75yn Unexpected ...blySecurity, StackCrawlMark& stackMark, Boolean forIntrospection)     at System.Reflection.Assembly.Load(String assemblyString)     at Microsoft.SharePoint.Workflow.SPWinOeHostServices.LoadWorkflowAssembly(SPWorkflowManager manager, String name)     
08/22/2013 21:58:36.54  w3wp.exe (0x10D4)                        0x1338 SharePoint Foundation         Workflow Infrastructure        88xr Unexpected WinWF Internal Error, terminating workflow Id# 46762e18-6042-43ef-82e1-24b8483e2275 
08/22/2013 21:58:36.54  w3wp.exe (0x10D4)                        0x1338 SharePoint Foundation         Workflow

Infrastructure        98d4 Unexpected 
                     System.ArgumentException: Object must be of type GUID.     at System.Guid.CompareTo(Object value)     at System.Workflow.Activities.CorrelationService.ValidateCorrelation(ICollection`1 initializerProperties, ICollection`1 followerProperties, String memberName, Activity activity)     at System.Workflow.Activities.InboundActivityHelper.ProcessEvent(HandleExternalEventActivity activity, ActivityExecutionContext context, Object msg, Type interfaceType, String operation)     at System.Workflow.Activities.InboundActivityHelper.ExecuteForActivity(HandleExternalEventActivity activity, ActivityExecutionContext context, Type interfaceType, String operation, Object[]& args)     at System.Workflow.Activities.HandleExternalEventActivity.Execute(ActivityExecutionContext executionContext)     at System.W... 
08/22/2013 21:58:36.54* w3wp.exe (0x10D4)                        0x1338 SharePoint Foundation         Workflow Infrastructure        98d4 Unexpected ...orkflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)     at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(Activity activity, ActivityExecutionContext executionContext)     at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime)     at System.Workflow.Runtime.Scheduler.Run() 
08/22/2013 21:58:36.59  w3wp.exe (0x10D4)                        0x1338 SharePoint Foundation         Monitoring                     b4ly High