I don't use Skype, so this is a response out of ignorance more than knowledge. One thing that sometimes works (I assume you've already tried powering off the phone and then turning it back on) is to clear the cache for an app. Start at the Home screen, then do Menu > Settings > Applications > Manage applications, scroll down to Skype, and tap it. There should be options to uninstall updates (as chase2hoop suggested), and also to clear data and clear cache. It's possible there's something "stuck" in the cache that's messing it up, and clearing it could fix it. However, since I don't really know anything about Skype, I don't know if this will work, and I don't know what it might accidentally delete (such as account information, which would have to be reentered). Proceed at your own risk!