How to Resolve The name 'xxx' does not exist in the current context Issue

Yesterday I was working on a page which contains Ajax Toolkit Tab Container, and there were some control on the other tab.

   

When i build my ASP.NET (C#) project in Visual Studio 2010, i started getting this error message

"The name 'XXXX' does not exist in the current context"

Displayed and the problem is in my .aspx page. Most surprisingly I can access the control in Intellisens but while compile time it throw error. My code definitely has no problem.

After debugging and searching for a while, i noticed that problem is cause by the back up copy of the same aspx file (copy of xxxx.aspx) that i forget to exclude from the project.

The problem solved after i exclude the file from the project.