Encountered the following problem today: When I wanted to open truecrypt I got the following error message: "truecrypt is already running". Solution
Most likely you did not close the application "cleanly" the last time you were using it. Now there is a lock file in you home directory.
Ok, open your home directory. Press CTRL + H (this will show the hidden files).
Now, there should be a file called TrueCrypt-lock-USERNAME.-DELETE IT.