I am sorry to hear about the error message on your PowerShot SX500 IS.
This error indicates an internal error has occurred. Sometimes this can happen if the battery runs very low while the camera attempts to power off. Please try using an alternate or fully charged battery in the camera to make sure this was not the cause. If the battery is fully charged, try removing it for a few minutes. If the error still displays on your camera, then it will need to be serviced.
To start the repair process, you'll need to complete a Repair Request on our website.
If this is a time sensitive-matter, additional support options are available at Contact Us.