It looks like you haven't mounted the TrueCrypt virtual device.
mount -t /dev/mapper/truecrypt1 /mnt/sda1
You should mount the TrueCrypt partition when you connect to it as follows.
truecrypt -t /dev/sda1 /mnt/sda1
It will ask you for the password. Then it will ask two other questions for which you can simply press the <Enter> key. The the partition will be mounted at /mnt/sda1.
You have probably noticed that all of this is done on a command line instead of using the TrueCrypt GUI. I hate the TrueCrypt GUI and it is easier to put the command line version in scripts.