Operation is not valid due to the current state of the object PS workflow

Dear All,

I've a situation here, whenever i create a project that has a custom workflow on it.  It threw an error "Operation is not valid due to the current state of the object"

Here's stack trace that i managed to get:

   at Microsoft.Office.Project.Server.Workflow.WorkflowHelper.GetService[T](ActivityExecutionContext context)     at Microsoft.Office.Project.Server.Workflow.ProjectSequence.SetInitialStages(ActivityExecutionContext context)     at Microsoft.Office.Project.Server.Workflow.ProjectSequence.Execute(ActivityExecutionContext context)     at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext)     at System.Workflow.ComponentModel.CompositeActivityExecutor`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()

Thanks and Regards,

Ariwibawa