This error occurs mostly when the Correlation Token values has been not set properly for activities.
Correlation token– A correlation token is essentially a means of uniquely identifying each instance of a workflow, modification or task.
OnWorkflowActivated, OnWorkflowItemChanged,OnWorkflowItemDeleted, SetState, SendEmail and UpdateAllTasks these activities should be using same workflow token for e.g. workflowToken.
CreateTask, CreateTaskWithContentType,UpdateTask, DeleteTask, CompleteTask,RollbackTask, OnTaskChanged, OnTaskDeleted, OnTaskCreated these activites should be using same correlation token for e.g. taskToken.
EnableWorkflowModification, OnWorkflowModified should be sharing same correlation token for e.g. modificationToken.
Each distinct task or modification would be having it own distinct token.