I know this is an old thread, but I just went through a lot of work to get a 64gb SDXC card to work with a 101b version S100. Here are some tips:
Swissknife does not do a good job of formating to fat32; FAT32 format works much better (and took about 1h 20 min for my card, but my card might have had issues) (FAT32 format would get to about 30% and then the percentage would start over, but the time would still tick down continuous from the starting time, very odd...)
If, after you go through all the steps at
http://chdk.wikia.com/wiki/Bootable_SD_card (Method 2 listed there, because my camera has no firmware upgrade in the menu) and the camera pauses upon a long power on push (like it should), but still says card is locked, use EOScard again to make the card un-bootable, then make it bootable again.
Hope that helps someone.
Steve