Access via 'NULL' object reference not possible

Hi All,

After APO upgrade, the get_instance method returnning NULL reference. Please help on this issue, what could be the reasons for that issue.

Details from ST22:

Runtime Errors         OBJECTS_OBJREF_NOT_ASSIGNED

Except.                         CX_SY_REF_IS_INITIAL

ABAP Program           SAPLY_BOP_BUFFER_LIST

Application Component  SCM-APO-ATP-BOP

Thanks,

Eswari.