Importing tracks of mixed recording modes doesn't work... MT1 into an MTP project.
In order to import those MT1 tracks into your MTP project, you first need to convert them to standard .wav format - doing this on a pc as blair suggests is probably your best solution, if the tracks you are trying to import are already on a CDR -
On the other hand, if you don't use a pc and converter software, I would assume that you could import those MT1 tracks from a CDR into a new MT1 project and then export them to .wav files all on your VS.
If the tracks are still on the VS in an MT1 project, then you can save a step and just export them to .wav file format onto a CDR..... then import the wav files to the MTP project.
Exporting .wav files on the VS can be tedious, as you may or may not have experience knowing. The pc route would be much faster, if there's a lot of tracks to convert to wav.
Once converted to .wav file and burned to another CD, you could then import them into the MTP project.