On Win7 64bit - update Sony Vegas version.
I loved the UT video codec - much better playback, lets my netbook play files that it would grind to a crawl on if they were lagarith.
I had SV Pro 8 32bit on my Win7 64bit system, and it never showed any 64 bit codecs as an option, so I uninstalled all 64bit codecs and it gave me LESS trouble, but still had rendering problems.
I would render a file (lagarith or Ut I do not remember) and the file would play fine on the machine and load into Vegas exactly as you showed here. If I used the 'Preview in Player' and saved it from there I got same results, but on opposite codecs - so I had to render one codec, and 'preview' the other and save from the player, then both would work.
And If I took file to work - same codec packs installed on 32bit Win7, same Vegas - the exact results again - but reversed. Media player could not render. but Vegas accepted them, no black frames! Drove me nuts. (These were both very new machines).
Compatability modes made no difference, no options I could find improved things. So I tried SV11 and all THOSE problems went away. All renders work fine, on machine and loaded into Vegas. (11 SEEMS to hate having large numbers of tracks, because it simply ignores most of them then. And when I do the pre-render, entire clips go dark for no reason I can figure out).
Never did get Ut working right, even latest version. Still gave me nothing but headaches so I dropped that as well. (Stopped rendering in it, left it installed so I could read files).