Problems exporting HD timeline in older Final Cut Studio HD

I've been working on an older version of Final Cut Studio HD. I had originally offlined the footage so I could edit it, and I finished onlining the footage with the original HD footage. The aspect ratio of the project and the footage is 1920 x 1080, and the codec of most of the footage and the timeline was set to H.264. The only problem is, now that it's onlined, it refused to render any of the transitions. It gives me some kind of codec error. I have also tried exporting the timeline as a Quicktime Movie, but it always fails at somepoint in the process. I have tried exporting Quicktime Conversion, and it failed too. The only way I was able to get it to output was to change the codec of the timeline and in Quicktime Conversion, but this provided a subpar quality file. I understand that I'm using and older version of Final Cut Pro on an older system, but I'm trying to find work arounds to this issue that will allow me to output a quality full HD file. Any help is appreciated.