Query without having to specify table's schema
If you want to go back to using the dbo schema like you were in SQL Server 2000, you can move the table back into the dbo schema:

ALTER SCHEMA dbo TRANSFER erpadmin.tablename;


An alternative if you like having the non-dbo schema is to set your user's default schema to erpadmin then if you do not specify a schema, it will use that as default. (Members of the sysadmin fixed server role ignore the DEFAULT_SCHEMA and use dbo by default.)

ALTER USER erpadmin WITH DEFAULT_SCHEMA = erpadmin;


The two part name you have (schema.table) is a good habit to get into though, so you can be explicit with which table you are referring to.  Some features require you to use a two-part name, Indexed Views are one example.