Problem with the taskflow invocation

If you face the following below error when rending the page, then the issue with the region with the task-flow:

java.lang.IllegalStateException: Attempt to validate an already invalid RegionSite

Solution is here:
Just set the following properties to the task-flow binding

go to bindings tab, select task-flow, then go to properties widow set
          activation: immediate,   Refresh: ifneeded