It's probably a browser problem I think Facebook uses a lot of Adobe Flash plugins, I had a similar problem with I.E. where it just stopped uploading halfway and froze. Try another browser dude or just wait and see if the images upload anyway despite the unavailable message...Jpegs are the best format to upload and make sure you dont move the file mid-upload, also you could try an image size reducer.
Facebook sucks anyways, everyone should open a skillpages.com, it's the career based version of FB. \m/
Skillpages - London, London, City of - Sinan Içoglu