I seem to encounter this error occasionally - when I try a simple search with the default parameters it happens consistently. Otherwise great addon! Using 3.6.15This review is for a previous version of the add-on (188.8.131.52-signed).
I couldn't reproduce the error.
Would you please disable other plugins and see if this still happens? How about check if you have the latest version of Craigslist Fusion? There is also a GreaseMonkey scrit for Craigslist Fusion that you can try. Thanks.