I don’t know how to tell Windows to stop logging it.
When unregistering it you will get more D+ alerts and I security is decreased some. I would not disable it just because it shows up in the Windows logs. When you want to be absolutely sure there is no harm done check the digital signature of guard32.dll to make sure it is the real deal.
Other than that don’t fix it when it is not broken. What’s more important a few entries in Event Viewer more or your system’s security?
Just remove the entry AppInit_DLLs and then guard32.dll will no longer load and no longer cause the error. I figure this is safe to do since I am not using Defense+ nor Sandbox. I checked the firewall functionality (inbound and outbound protection) with guard32.dll disabled and it still works perfectly.
You can also toggle the AppInit_DLL’s on or off with the “Autoruns” tool, by removing or replacing the appropriate checkmark under the AppInit tab. Very straightforward.