Symptom 

I'm running running ESET Remote Administrator 2.0.56. After upgrading from the trial to the purchased version, I started receiving the event below in my Application Event
Log.

Source:  ERA
Event ID:  502
Type:  Error
Description: The description for Event ID ( 502 ) in Source ( ERA ) cannot be found. The local computer may not have the necessary registry information or message DLL files to display messages from a remote computer. You may be able to use the /AUXSOURCE= flag to retrieve this description; see Help and Support for details. The following information is part of the event: Error: Update failed, code: 4, additional code: 8193.

Solution 

Here's the solution provided by ESET support:

1. Open the Remote Administrator Console (RAC).
2. Go to Menu >> Tools >> Server options... >> Updates tab.
3. Make sure you have the correct user name and password.
4. Click on Update Now button.

Sure enough, although I had updated the username and password in the 2.7 mirror setup, I had forgotten to update them in the RAC as well (where the 3.0 mirror is configured). Once I made that change, the errors stopped appearing in my event log.