Catch the WorkflowValidationFailedException exception when loading the workflow and iterate through the Errors collection to see what is wrong.

Dim workflowInstance As WorkflowInstance
Dim reader As XmlReader = XmlReader.Create("workflow.xoml")

Try
		workflowInstance = workflowRuntime.CreateWorkflow(reader)
		workflowInstance.Start()
Catch ex As WorkflowValidationFailedException
		For Each ve As ValidationError In ex.Errors
				Console.WriteLine(ve.ErrorText)
		Next
End Try