There were a number of cases of this error reported back in the 12.5.x days. I don't think a root cause was ever found. In general, people increased the sp_configure "number of alarms" setting (though that wasn't enough on its own to stop the error once it had started happening) and rebooting ASE (which did clear the condition). i.e. reboot to clear the error, and perhaps increase alarms to reduce the chances of it happening again in the future.