When upgrading from Enterprise Server 8.0PE to 2.1, an error is thrown saying the server does not have system connector named null, and invalid user information as seen in sbs-manual. Even after changing the hardcoded values, the same error message is seen.
You can only encounter this bug while upgrading from a 8.0 PE toEnterprise Server. The workaround is to upgrade to either 8.1, 8.2, or 9.0 and then upgrade to Enterprise Server.