Problem with Creating Activex Controls in Visual Studio 2008

When we  add a control (ex.   ) to an ascx or aspx
file, visual studio is supposed to automatically add the definition for that
control to the designer.cs file (associated with that ascx or aspx). But it
is not added or updated properly in VS2008

It seems most of the developers are  facing this issue.

We need to regenerate the designer class to solve this issue

To regenerate the .designer.cs file for a ASPX/ASCX, first delete the
.designer.cs file, then right click on the ASPX/ASCX and click "Convert to
Web Application".  This will probably give you an error message that will
help you find the root of the problem.  I noticed that there's a difference
in the error message you might get here versus  the file that is being
opened in the Design mode in Visual Studio.

For example, we had a .ASPX file where the .designer.cs file was not being
generated when we modified it.  We could not figure out what the error was
until we discovered this tip because Visual Studio did not give us any
feedback.  Once I deleted the .designer.cs and ran "Convert to Web
Application" on the file, I was prompted with an error message that informed
me that we had a <%@ Register /> declaration in our ASPX that was also
declared in our web.config file (and this was creating a conflict even if
they both pointed to the same location).  Visual Studio could benefit from
better error reporting for this particular scenario.