I would like to select images from an external hard drive. When I attempt to select the folder on the hard drive, it isn't recognized by the andreamosaic page...and I've connected other external hard drives to see if it was specific to that one...it's not. Any ideas?

The external disk (even a network disk) should be seen like a local disk C:, D:, F: and so on.
If it is shown only as a path \\my external disk\\my folder then probably it won't work.