I tried to run the script, so that when ever I restart the freebsd, the script should run automatically, I kept that script in /etc/rc.d/ and gave full permissions, it is not executing but it is saying:
eval: truecrypt not found
but when I am trying to run manually it is been executing.
I kept the script in one location and password in other location.

When you run the script successfully, do a
which should give you the full path of the truecrypt executable, then specify that full path in place of your
truecryptcall. Potentially make sure the file is accessible.