Hi,
I also gone thru same error because of new calendar created and assigned to existing PSA.
I regenerated WSR from Back dated but be cautious while regenerating WSR if you have created new holiday calnedar (you have to assign last year holidays to new cal) nywyz this will be applicable if you have created new hol cal.
you can recheck the scenario by clearing master data change and PDC date
Regards,
Jay