Diagnosis
Only the start or the end of the XPA LOOP - XPA ENDL loop is in thissubschema. The other part is missing.

System Response
If the start or end of the loop is in the main schema in which thissubschema is contained or in a different subschema within this mainschema, no error occurs.
If the start or end of the loop is completely missing, an error messageoccurs in the main schema.

Procedure
You can save the subschema. Then check the main schemas in which thissubschema is contained.