SQL Database Mirroring Error: 1443, Severity: 16, State: 2

Hello, I am trying to mirror two databases and i receive the following error to the principal error log. "Error: 1443, Severity: 16, State: 2 ".

I HAVE:
1) SQL server 2005 enterprise SP2
2)ServerA And ServerB in the domain.
3)I have installed both ServerA and ServerB sql server with network system account and the services run both as NT AUTHORITYNETWORK SECURITY.
4) The principal database "Test" is on ServerA, i create a full backup and log backup and restore to ServerB the Full backup and the Log with NORECOVERY.So the database "Test" in ServerB is Restoring......
5)I Have created to both Servers Endpoint to Port 5022 with AUTHORIZATION=NT AUTHORITYNETWORK SECURITY.
6)The endpoint are both operational (I have tested through telnet command)....
7)I have added NT AUTHORITYNETWORK SECURITY user to both Security>logins and i gave full permittions sysadmin to the user.
8)I am executing the query "Alter database [TEST] set partner= N'TCP://xx.xx.xx.xx:5022'";
successfully from ServerB (Mirror) but from ServerA i receive that error!!!!

I believe it's network account security issue, but i cannot find a solution for that..... (I also tried to add DCServerA$ user to logins on ServerB AND DCServerB$ user to logins on ServerA cause previously i recaieved an login security error!!!)