Mount problems

df-h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda5       240G  123G  105G  55% /
udev            3.9G  4.0K  3.9G   1% /dev
tmpfs           3.9G  192K  3.9G   1% /tmp
tmpfs           1.6G  1.2M  1.6G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            3.9G  408K  3.9G   1% /run/shm
none            100M   36K  100M   1% /run/user
tmpfs           3.9G  1.1M  3.9G   1% /var/log
tmpfs           3.9G     0  3.9G   0% /var/tmp
/dev/sdc2       961M  435M  527M  46% /media/usb0
/dev/sdc1        14G   12G  2.8G  81% /media/usb1


kasual@kasual:~$ mount /dev/sdc1
mount: according to mtab, /dev/sdc1 is already mounted on /media/usb1
mount failed
kasual@kasual:~$ mount /media/usb1
mount: according to mtab, /dev/sdc1 is already mounted on /media/usb1
mount failed