When you Setting Database Mirroring if you will get the error message like "The mirror database has insufficient transaction log data".
The mirror database, "Northwind", has insufficient transaction log data to preserve the log backup chain of the principal database. This may happen if a log backup from the principal database has not been taken or has not been restored on the mirror database. (Microsoft SQL Server, Error: 1478)
Error : The mirror database has insufficient transaction log data
1.. Take the Transaction Log backup from Principal server database and
2. Restore Log on Mirror database
Restore Log on Northwind from disk = 'c:\mssql\backup\DBP_TLog.TRN' with NORECOVERY
3. Now try to setting up Database Mirroring again from Principal Server