First thing I would do is use HD500 Edit to back up your presets/setlists.
Then reinstall the latest firmware, choosing to replace the existing presets. This will guarantee that you have a compatible set of factory presets in the HD500. This should avoid any DSP overload, and should allow you to use the device normally. Once you are satisfied that the device is working properly, try reloading your saved presets/setlists one at a time. Any presets that generate the error message should be edited to remove some of the excess DSP requirement.