Try to query a remote table through a database link:
SQL> select count(*) from testuser.test@dblink_test; select count(*) from testuser.test@dblink_test; * ERROR at line 1: ORA-02085: database link UDBLINK_TEST connects to TESTDB
REASON
Check database parameter global_names =TRUE. If parameter global_names =TRUE, the database link name has to match the remote database name( TESTDB).
WORKAROUND
Turn off global_names in session level, then it should be ok.
SQL>alter session set global_names=false; Session altered. SQL>select count(*) from testuser.test@dblink_test; COUNT(*) ---------- 100