For the benefit of Raylight Ultra users who find that it doesn't work with with Sony Vegas Studio HD Platinum 11 (V11):

This is what happened in my case:

1) I installed my upgrade V11 thinking it will replace 10, but realized after it was done that it was a side-by-side install.

2) I uninstalled V10.

3) I Reinstalled Raylight Ultra, and ran V11 but MXF import didn't work.

4) Within minutes (long live the internet and thanks, Wadro65!) I ended up on a related thread in these forums and found this set of instructions meant for Vegas Pro users:

*** START ***

1. Install Sony Vegas Pro 11.
2. Install Sony Vegas Pro 10 full or demo version.
3. Install Raylight Ultra.
4. Go to C:\Program Files\Sony\Vegas Pro 10.0
5. Scroll down to find and copy file, DVFilm.fio2007-config
6. Go to C:\Program Files\Sony\Vegas Pro 11
7. Paste config file into this folder.
8. Launch Sony Vegas Pro 11. and you should be able to open .mxf files.
9. You can now uninstall Sony Vegas Pro 10 full or demo if you wish.

*** END ***

5) Before reinstalling V10, I did a search to see if the config file was present on my system, and indeed it was (even after I had uninstalled V10).

6) I copied the file as instructed above and ran V11.

7) MXF import is working as intended, without issues.

Conclusion: if the file is already present, just copy without reinstalling the earlier version.

Hope it works for you too :-)