ASP.NET MVC Unknown server tag error

I was wondering why could I have not caught this issue in local testing? I am using a Content Panel user control in all my user controls. In one of the us开发者_高级运维er control I missed the register tag for Content Panel UC. While testing locally all things were working fine . Suddenly on our QA box I got a critical issue. Application was throwing Unknown server tag 'cc1:ContentPanel' in the Landing page.

Can anyone explain why it was not caught locally?

Most likely there is a mismatch in your web.config files.

Use a diff program to compare the web.config on QA against the web.config on your box.

I bet you'll find the problem there...