I'll start with http://forums.macrumors.com/showthread.php?t=451744
Most photos are far too big today for craigslist so give yourself time to learn about external hosting (I use photobucket) or how to export and resize such (read link).
I also have been going crazy trying to choose a photo from Iphoto, After I get the ad posted I click on the (add/choose photo) and it takes me to the Finder list with 4 different things to choose from for the pictures. I can't get any one photo. It takes me to the whole file that is entered as the photo and consequently will not load as file is too large.
I just used to click on the (add/choose photo) and it would let me make a choice of what photo I wanted or type in the file link to get the photo.
Please help. Geek Squad was no help even with the 2 year warranty I have with them. Did not fix the Problem.