Unrecognized attribute 'xmlns'.

(8 May 2012)

Problem

ASP site says: Unrecognized attribute 'xmlns'.

...usually in reference to some file which ends "web.config" line 2.

Solution

You might receive this error when you have multiple versions of .Net Framework.

Resolution:

• Launch IIS
• Go to the properties page for the application.
• Select "Asp.net" tab, and change the Target Framework to 2.0.

(In my case, changing it to 2.0 did nothing but render the site totally 404 -- but happily(?) I also had 4.x installed, changing to that fixed the problem.