I am not quite sure but see if your problem is due to this bug http://web.archiveorange.com/archive/v/RybTrtkbz0vNyQrK1IlX
That said what you are doing even without bugs, is fraught with potential output disasters, PDF is a complex document format usually not intended to be converted to other formats, it is principally for display and printing as is.
Text and picture extraction is easy with the same tool you mentioned without the -c switch which tries to preserve the look of the original PDF,
I would say try to convert without using the -c switch,this will likely get you good enough images but the layout may not be what you want, but maybe you could create something to fix it up. you may not have to fix anything if the PDF is simple.