Trouble backing up Windows 7 onto a truecrypt external HDD

Encrypted a HDD with truecrypt.

{{{Look at the Back up problem 1 screenshot

On

Create a system image > Where do you want to save the backup?

under "On a hard disk" radio button

when <Refresh> is clicked... }}}

{{{ Look at the Back up problem 2 screenshot

...... the "Create a system image" with "Looking for backup devices..." appears

Unfortunately, the truecrypt hdd does not appear under the "On a hard disk" radio button's drop down menu..... }}}

{{{.....Therefore the "On one or more DVDs" radio button is filled up (See Back up problem 3). My OS is too big for DVD back up. }}}

How do I make the truecrypt hdd appear under the "On a hard disk" drop down menu so that the entire OS can be backed up onto it?