Development on TrueCrypt has been stopped and so it is a good idea to uninstall TrueCrypt and switch to other alternatives. Since TrueCrypt is not installed from a package, you might have forgotten how to uninstall it.
First make sure that you have unmounted all TrueCrypt volumes.
Uninstall TrueCrypt using the script it had placed during installation:
$ sudo /usr/bin/truecrypt-uninstall.sh
Tried with: TrueCrypt 7.2 and Ubuntu 15.04