Ah, I had this same problem. This happens because of 64bit doesn't like the walking method for some reason.
To solve this, I had to follow this tutorial: http://www.rune-server.org/runescape...n-jre6u14.html
If that still doesn't work, uninstall Java, and install 32bit java instead. If you do this, and you are using an IDE such as Eclipse, you will also have to download a 32bit version.