is this true on mixed media project?
Set RAM Preferences
These settings will reduce the amount of memory used when scrubbing or rendering. The Dynamic RAM preview is not needed with Ultra and can interfere with switching between low and high quality modes. In Vegas, click Options->Preferences and select the Video tab. Set the Dynamic RAM Preview max to 0 (zero). Also most HD codecs are already multi-threaded so only one rendering thread is needed, this will also reduce memory use and improve performance. Set the Maximum number of rendering threads to 1 (one).
http://dvfilm.com/raylight/ultra/UltraVegas.htm
Set RAM Preferences
These settings will reduce the amount of memory used when scrubbing or rendering. The Dynamic RAM preview is not needed with Ultra and can interfere with switching between low and high quality modes. In Vegas, click Options->Preferences and select the Video tab. Set the Dynamic RAM Preview max to 0 (zero). Also most HD codecs are already multi-threaded so only one rendering thread is needed, this will also reduce memory use and improve performance. Set the Maximum number of rendering threads to 1 (one).
http://dvfilm.com/raylight/ultra/UltraVegas.htm