Check sum errors may come from the battery-backed ram. If your software allows it, try setup/service/fix, which will cure a bad checksum. If it reappears after powerup it is almost certainly the battery.
If you need a battery, see http://eventidestore.com/insrme1.html – note that they are not cheap. They usually last about 10 years, so given the age of any DSP4000, it might well be the cause.
