.MP4 files NOT working in Sony Vegas 11

[hbaws]

Hey, this is my first time posting here, so sorry if I post in wrong section and what not. I hope this forum can help me, anything is appreciated

I wanted to begin an AMV project today, so I decided to research on how to convert .MKV files to import them into Vegas 11.
So I decided to do some research and I came along a quite helpful video: http://www.youtube.com/watch?v=gsDndcvglrA

Read bold for summary.
Anyway, I managed to convert my .MKV files to .MP4 files removing subtitles using a program called MKVToolNix, and MP4Box. When converted to MP4, it didn't kill the quality of the video one bit so I loved it!
Until ... I tried to import it to Vegas and it immediately crashes. Upon crashing, it gives me a message "Vegas has stopped working" and gives me the option to 'send' the error or not to.
Now I'm sorta frustrated because I could import OTHER .MP4 files but not these ones, and I don't know why. I then decided to convert the .MP4 files (the ones that were originally .MKV's) to .MP4 itself but it just totally destroyed the quality.
Now I'm frustrated, and I hope to get some help. Could this be a codec problem? Anything?
Is there another way to extract subtitles off footage and make them compatible with Vegas?

Thanks in advance.

[mirkosp]

read AbsoluteDestiny & ErMaC's Technical Guides to All Things Audio and Video.
Ideally, you should open the mkv in virtualdub through an avisynth script. Use ffvideosource for that (be sure to grab the latest, the avtech is rather old on that side). After you have your avs ready to be opened in virtualdub, making lossless avi clips (or just converting entire episodes if you have the space for it) with UT Video as the codec (pick ULY0 from the four in the list) is the last thing left, and after that is done you can load that avi into vegas safely.

[Animated]

...I bet he didn't understand a thing...

[mirkosp]

Well, in order to understand the post, he actually has to read the guide first... which is why I linked it.