I have two servers running SharePoint 2013 and both were getting the same Event ID 8321 error every 15 minutes or so in the Event Viewer:
A certificate validation operation took 15004.9996 milliseconds and has exceeded the execution time threshold. If this continues to occur, it may represent a configuration issue. Please see http://go.microsoft.com/fwlink/?LinkId=246987 for more details.
I made two changes to solve this, not sure which one did the trick finally but both are worth trying. The first, my company uses a proxy server, but I didn't have this configured on either server. The second was to download the latest (December 2012) Root Certificates from Microsoft here: http://www.microsoft.com/en-us/download/details.aspx?id=35945
So far no more 8321 errors, if they do come back I'll let you know!
Updated 5/6/2013...well, turns out it was the first trick that solved this. My company uses a proxy server to connect out to the Internet, but it's set up with a configuration script. So...the fix is:
2) In HKEY_USERS, for each SID based ID (not with _Classes) drill in to:
3) Create two keys:
AutoConfigURL, string, set the value to your config script URL
ProxyEnable, DWORD, set to 0
Reboot for good measure. This did work for me, no more of those pesky errors.
Found this Support article describing a fix which adds the SharePoint certificate to the trusted certificates store on the server: http://support.microsoft.com/kb/2625048