An older version of the transaction 820 schema was previously included with BizTalk Server. Therefore, this hotfix has the same doctype as the existing transaction 820 schema. The new and old transaction 820 schemas cannot coexist in a BizTalk deployment . If both of the transaction 820 schemas have to be used in a BizTalk deployment, you must change the namespace of the new schema so that both schemas can be uniquely identified and used in the BizTalk application. In this case, the new schema has to be treated as a custom schema.