@fuko it's the sand and a stuck lens is one of the most common errors with any digital camera. Take a look [link|http://camerarepair.blogspot.com/2007/12/fixing-lens-error-on-digital-camera.html|on here] for some ideas on how to possibly fix it. Most of the time the only thing to do is to replace the lens. Use this guide [guide|92002] to replace the lens. As for a repalcment, do an online search and see if you can find a suitable lens.
Individual repair parts for a lens assembly are extremely difficult to find, but of course you can always try.