If TrueCrypt appears to freeze on your first attempt at mounting a volume after system start up, then you probably need to create a loop device. Indeed, if you wait long enough you’ll receive this error message from TrueCrypt:
Failed to set up a loop device
The solution is documented on the Arch Linux wiki: https://wiki.archlinux.org/index.php/TrueCrypt#Failed_to_set_up_a_loop_device
A command for creating a loop device is:
mknod -m 0660 /dev/loop8 b 7 8
Run the above command as root before attempting to mount your TrueCrypt volume and it should mount correctly.
To avoid having to do this upon each reboot before you use TrueCrypt, you might like to set some loop devices to be automatically created at startup:
echo "options loop max_loop=8" > /etc/modprobe.d/eightloop.conf