Does the problem happen on all the PCs on your network?  How about trying it on the server itself using the real address or localhost?  What URL do you use?  Is it available externally?  Could you be having DNS issues?  How about different browsers?  Do you have your site in the "Trusted" sites zone? 

All this sounds like an issue with aliases and/or host headers.  By the way, after making any changes to the configuration I always do IISReset and close the browser just to be sure everything is refreshed.  You may also try looking into the IIS logs.

Carlos

There will a record of the problem in the log files, especially if you know it was after the update, you will know where to look. It could be something as simple as a reboot or something deeper such as a dependency, service not being available, or metabase corruption. I have watched aspnet_regiis adjust issues especially with custom machine.config.

One quick way tro check is to uninstall IIS and reinstall it.There is always a reason. Event logs will prove it.