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I recently installed a MediaWiki installation on my IIS. Most of it worked, but every time i wanted to create a new page or click on a red link, instead of the “edit this article” page, a “404 page not found” error was shown.

This is a problem with IIS misconfiguration, see Bug 18270 in the wikimedia bugzilla. Comment 19 solves this issue:

Got to IIS Manager.
Open Web Sites.
Right click on the website and select Properties.
Go to the Custom Errors tab.
Scroll down to the 404 error, select it and click the “Set to Default” button.

Hope this will help someone Cheers!