Brutal formatting on the post, though...

Congratulations, you just fixed your player. The error you
saw was normal use. You should be all set at this point.

What you did was use what portion of the build worked (root,
swap and scratch) to get into the player and build the music
filesystem by hand. The error you saw about the filesystem
already mounted was because (I forgot) the rwm would have
remounted /drive0 read/write. This would have worked since
the filesystem was then built at the time.

You should be fully functional at this point. You may just
want to do an fsck set when you get time, just to clear the
marker on the root partition.

Edit: Tony - a recommendation for the disk upgrade FAQ. If
people cannot build their new drives due to memory limits,
this procedure can be used to finish the build job. This
worked on a Mark2 with a 100GB drive - it might work with a
Mark1 as well. As drives get bigger, this will be more
common.