Satish,
HG is not an SAP standard availability check. Please show me the OVZ2 settings in ECC for this custom check.
With respect to the MARC-APOKZ entry, this is normally maintained by creating and activating the appropriate integration models (Material integration model and also the ATP integration model). You should probably re-create and re-activate these two integration models for this material. CFM1 & CFM2.
Best Regards,
DB49