@Will - That's the trigger! With the attribute runAllManagedModulesForAllRequests="true" added to the <modules> node of <system.webServer> I am now able to reproduce the issue. It all makes sense - the DotNetNuke UrlRewriteModule is now forced to process all requests including those for image files, etc. Since .png and .ico extensions are not specifically excluded from further processing as are other image file types, .axd's etc., in the module's code, the newly added code for automatic addition of portal aliases sees each request for a .png and .ico file as a new portal alias and merrily addes them to the PortalAlias table. In addition, these image files are never properly served resulting in their disappearance.

Now, the question I have is how did it come about that the attribute runAllManagedModulesForAllRequests="true" is being added to the <modules> node of web.config on a new install? I can see that it might have been added manually or by a third party extension in a prior version to get around the issue of a module not running. I do not see that attribute being included in the <modules> node in any of the DotNetNuke install or source packages.

As a fix for now, seems to work:

1. Remove the runAllManagedModulesForAllRequests="true" attribute from the <modules> node of web.config.
2. Delete any erroneous portal aliases from the PortalAlias table of the database
3. Revisit the site in your browser.

If you had added the runAllManagedModulesForAllRequests attribute because a particular module was not running, the removal of that attribute would be expected to cause a return of that issue.

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Bill, WESNet Designs
Team Lead - DotNetNuke Gallery Module Project (Not Actively Being Developed)
Extensions Forge Projects . . .
Current: UserExport, ContentDeJour, ePrayer, DNN NewsTicker, By Invitation
Coming Soon: FRBO-For Rent By Owner

I think there are two separate issues going on here... I'm in the same boat as Rick Parsons... the "runAllManagedModulesForAllRequests " attribute isn't set in my web.config, I don't have a bunch of bogus PortalAlias entries, and browsing to the domain without specifying a page brings up the "Windows Vista" error (but browsing to a specified page works fine.) This site is set for .NET 4.0, but I have another site on the same shared host that is set for .NET 3.5 that works fine. I don't think this problem has to do with PNG files.