Comment 2 for bug 134883

I got the same thing. Here is my report:

Not a serious problem, but may be annoying.

Towards end of installation, I got a warning dialog saying:
------------------------------------------------------------------------
migration-assistant needs to mount a partition, but cannot do so because
the following mount point could not be unmounted:

/mnt/migrationassistant

Please close any applications using these mount points.

Would you like migration-assistant to try to unmount these partitions
again?
------------------------------------------------------------------------

At that point, on terminal-shell I did:
  # mount
that gave the following output.

------------------------------------------------------------------------
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
tmpfs on /lib/modules/2.6.22-12-generic/volatile type tmpfs (rw,mode=0755)
tmpfs on /lib/modules/2.6.22-12-generic/volatile type tmpfs (rw,mode=0755)
varrun on /var/run type tmpfs (rw,noexec,nosuid,nodev,mode=0755)
varlock on /var/lock type tmpfs (rw,noexec,nosuid,nodev,mode=1777)
udev on /dev type tmpfs (rw,mode=0755)
devshm on /dev/shm type tmpfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
/dev/sda3 on /target type ext3 (rw)
/dev/sda6 on /target/home type ext3 (rw)
/cdrom on /target/media/cdrom0 type none (rw,bind)
/dev/sda1 on /mnt/migrationassistant type fuseblk (rw,nosuid,nodev,noatime,allow_other,default_permissions,blksize=4096)
------------------------------------------------------------------------

I believe it was while trying to get user-data from Windoz-partition.