uploading pics to Craigslist from the iPhone

I have an account on craigslist and post ads a few times a day. I can post the entire ad but cannot upload pictures from the iphone. When I click add/edit images the 4 boxes with the red x come up but the 'choose images' button cannot be selected. Does anyone know if it's possible to upload pics to craigslist from the iPhone? Any other suggestions? Thanks!