I had the same problem "way back in the old'en days" when the A720is was first ported... Turned out that the file system was not creating the directory structure and default files (they added a delay to the code).
Probably using an external card reader, do you see:
CHDK/CHDK.CFG
Plus the following directories under CHDK:
BOOKS
FONTS
GRIDS
LANG
SCRIPTS
On the original A72is build, I just had to create the directory structure and then the camera worked fine after than (was fixed around build 23--back around January 21, 2008...
Also, it is possible you have a corrupted CHDK.CFG file... You can try deleting it and setting your preferences.
-Bill