The remote copy of database x has not been rolled forward to a point in time that is encompassed in the local copy of the database log
Make sure you disable existing log backup job that is automatically backing up the log file.
The only thing that I can think of is that maybe there is a job that is automatically backing up the log file on the principal?
Generally you have to backup one log file and restore it on the mirror before you can setup mirroring. Also, any log backup you do since the full backup must be restored on the mirror.
But basically the error message says it needs more log. Go ahead and backup the log again, restore it and try again.