I recently ran across an error where TrueCrypt wouldn't start on my computer running Arch Linux. When I tried to run TrueCrypt graphically nothing would happen, but when ran from the terminal I received a message telling me that "TrueCrypt is already running". This error is caused when your last TrueCrypt session didn't close cleanly and left a lock file behind in your home directory.

To remove the lock file just run (Replace YOURUSERNAME with the username for your actual account): rm ~/.TrueCrypt-lock-YOURUSERNAME

You can also navigate to your home directory using a file manager and deleting the file graphically. If the file is hidden, you can show it by pressing Ctrl+H in your file manager.