I've heard of problems like this before.
I use Protools LE so i'm pretty familiar with the procedure however the free version has some limitations and this is one of 'em.
From what i've heard those of my friends who use PT Free import their trax after converting'em to QuickTime Movie , meaning if u have .AIFF, .WAV open these files using the Quicktime player then save 'em as QT Movie.
If it's an mp3 file get the SoundJam (basic is free - mp3 player) convert the mp3 to AIFF or WAV then to QuickTime.

Luck