To all reading this thread:
If you elect to follow expert Rahul's suggested workaround, be aware that deactivating the ATP integration models in the way he suggests means that ATP will be reverted to the Availability checking within ECC during the period that the ATP model is deactivated.
Depending on the amount of ATP activity, and the type of GATP that was implemented in SCM, this would probably lead to sales orders with confirmations that do not meet business requirements. Careful evaluation of this solution is necessary before implementing in production.
Best Regards,
DB49