Web.config Configuration An Extension of Name "SecurityServiceBehavior" already appears in Extension Collection

The following error on your web app can be due to multiple reasons, however the root issue is because your web.config is being loaded twice. The error is does not indicate that you have duplicate tags in the web.config nor that its an issue with this specific tab. How does the web.config reoload twice? One is something within your code where when you get to your webapp, it can do some other function or loging that calls your web.config again. Another reason in my specific case was due to incorrect IIS settings on the web app for example:

The root on website test.com has an application declared with home:


d:\intepub\wwwroot\test\virdirectory instead of just d:\intepub\wwwroot\test
Then there is a virtual directory off the root of test.com called virdirectory with a  home directory of:

• d:\intepub\wwwroot\test.com\virtualdirectory

This causes the web.config to be loaded twice.

James Chong
MCITP | EA |EMA; MCSE |M+, S+
Security+, Project+, ITIL
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