Urgent! Please help get past errors.......

I am attempting to setup mirroring. I backed up my prinicipa db and restored it to mirror, choosing With NORECOVERY.
Now when I try to start mirroring I get:
'The remote copy of database "MyDB" has not been rolled forward to a point in time that is encompassed in the local copy of the database log"
Also, when I tried before I got:
"A error occurred while starting mirroring and the server network address can not be reached"
Please advise! THX
UPDATE: I think I'm good for now. I forgot to backup and apply the t-log.

Seconf message must be due to network issue like DNS naming incorrect of server or it must have been not open for communication.
When got that message did you try ping the mirror from principal server or other way around ?
Regards
Sat

Thx. Your assessment sounds right. We changed the name of the DR server, and needed to flush the dnscache.
All is working now...