JVM 517 error means that your system file is corrupted. the only options you have is to re-install the device software, or boot into safe mode to see if you can uninstall whatever app caused the corruption. unfortunately, nothing about being able to do back ups when the error occurs.
looky here at the link on the 2nd post---->
JVM Error 517 - BlackBerry Forums at CrackBerry.com
rule of thumb: always do a back up of your phone.