If you get the following error in the event log:
Unable to find event description for Event ID 56. OS reports the message resource is present but the message is not found in the string/message table.
Event Source: Application Popup
Event ID 56
It’s probably because you have a popup that’s happened during an uninstall, and the uninstalled program has it’s own event log additions that are no longer available as it’s been uninstalled.
In short, it’s nothing to worry about.