SQL & PL/SQL

i try to create a global database link through two databases MZFB et MZF14952.
the MZFB database is installed under the machine MZFXPDESK
the MZF14952 database is installed under another machine SUPPORT1

i execute this code
CREATE DATABASE LINK dbl_14952_5
CONNECT TO BELGA_5
IDENTIFIED BY mypwd
USING 'MZFB'

select * from dba_db_links
OWNER DB_LINK USERNAME HOST CREATED
MZF14952 DBL_14952_5.CORP.MYCOMPANY.COM BELGA_5 MZFB 02/14/2007 14:17:21:000

select * from global_name
DBL_14952_1.CORP.MYCOMPANY.COM

select * from all_users@MZFB.CORP.CASTSOFTWARE.COM
=> ORA-02019: connection description for remote database not found