We can't know. You have not provided any system information, no details about your file, where you are trying to save them or even what version of PS you use. Sorry, this is pointless. You need to be much more precise and provide the necessary technical details.
There should be an X in a circle next to the "saving 0%". Click it.
Try saving again after. If that doesn't work, try saving in another format or try saving another image in the same format. Could be just a hiccup or maybe even a corrupt file format plug-in.