yeah, like elephantinc said, you probably are rendering them without a file extension (do you view stuff in finder with that showing?)
however, i don't know how to change the file name of multiple files using Terminal (or command line for that matter) so unless you know a way render it all out again
in your render globals what's the file name you're rendering out to?
it should look something like this:
where images/Master Layer/ is the directory that you're pictures will end up in and myImage0001.png is the same of the file it's outputting
also you can check the progress of the batch render by opening up the script editor, when it seems like it's crashed it might actually still be doing stuff
that's a "Ch" pronounced as a "K"
Computer skills I should have:
Maya, XSI, Photoshop, AfterEffects, Motion, Illustrator, Flash, Swift3D