problem mounting encrypted external usb harddisk with ext3

I want to mount my external usb harddisks (under SuSE 9.3 formatted with ext3 and encrypted with twofish256) under opensuse 11.0 , but it doesn’t work.

First I use
losetup -e twofish256 /dev/loop0 /dev/sdc1
and type in my password and then I try to mount with
mount -t ext3 /dev/loop0 /media/TREKSTOR6

The kernel log says
kernel: VFS: Can’t find ext3 filesystem on dev loop0

The strace-output of the mount command gives my the output

readlink("/dev", 0x7ffff8b24720, 4096) = -1 EINVAL (Invalid argument)
readlink("/dev/loop0", 0x7ffff8b24720, 4096) = -1 EINVAL (Invalid argument)
stat("/sbin/mount.ext3", 0x7ffff8b263c0) = -1 ENOENT (No such file or directory)
rt_sigprocmask(SIG_BLOCK, ~[TRAP SEGV RTMIN RT_1], NULL, 8) = 0
stat("/sbin/mount.ext3", 0x7ffff8b263a0) = -1 ENOENT (No such file or directory)
mount("/dev/loop0", “/media/TREKSTOR6”, “ext3”…, MS_MGC_VAL, NULL) = -1 EINVAL (Invalid argument)
rt_sigprocmask(SIG_UNBLOCK, ~[TRAP SEGV RTMIN RT_1], NULL, 8) = 0

Is here the problem?
Why does not exist /sbin/mount.ext3 (and in fact, it does not exist in my file system)?