this is a case sensitivity issue. you have 2 diferant cart opjects:
1) new_ProRes
2) New_ProRes
looks like the lower case n object:
new_ProRes
is the one being used most of time. at line 7 of the store page, though, it uses the upper case N version:
require_once("WA_eCart/New_ProRes_PHP.php");
I changed that to:
require_once("WA_eCart/new_ProRes_PHP.php");
which fixed the problem.