Proc errors because:
1) the script was not made to disable images in Settings.ini (Background, Background2, Banner and Icon).
What you could do: Just crate 1x1 px black bitmap images.
Also in script don't disable images (WizardImageFile=, WizardSmallImageFile=).
If you want a non-image minimalistic installer, you could try out this:
http://fileforums.com/showthread.php?t=99549
2) if you want to use UltraARC, just enable it by removing ; . Do not replace it with enabled DiskSpan define. In this case, DiskSpan is enabled too alongside with UltraARC, which gives you proc errors too (because there is no #define DiskSpan, so all #ifdef DiskSpan will be compiled too).
3) Weird stuff is a bug in script, will fix it soon.