In most cases, the description for this event is shown as:
The description for Event ID ( 5050 ) in Source ( IAS ) 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: .<domain controller name>, <domain name>.
However, the event in itself is just an informational one confirming that the IAS was able to connect with the domain controller. The description is not displayed correctly because of a blunder from Microsoft in setting the proper event log message file for the IAS service (see the "What is the event source?" article).
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