You must specify a primary site before you can modify a default error class.
Initially, rs_sqlserver_error_class and the other default non-ASE error classes, do not have a primary site. Since you can only create server-wide error classes at a primary site for a class, use create error class to designate one of the Replication Servers as a primary site for an error class.
For Adaptive Server for example, execute create error class rs_sqlserver_error_class at the primary site. Verify that all other Replication Servers have direct or indirect routes from the primary site.