It may not help--but take the SD/SDHC card, place it in you card reader and find the CHDK.CFG file (it contains all of your CHDK settings).
Either move it back to your computer, rename it CHDK.OLD or erase it (depending if you need to save your old settings or not.
When you restart the camera, (remembering to change the write protect switch on the card), CHDK will create a new CHDK.CFG file--see if this works or not. It is possible the old CHDK.CFG is corrupted or has some setting messed up.
You could also try setting CDHK back to its defaults.
-Bill