ASP.NET Page says I need to reference an assembly that does not exist!

Attempt 1:

A similar question was asked a couple of months back and look at those answers.

Attempt 2:

Have you cleared the "Temporary ASP.Net Files" for the site, usually found at C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files? There may be an old copy lingering around.

For some special cases you could get rid of this if you disable batch compilation in the Web.config file like this:

<system.web>
    ...
    <compilation debug="true" targetFramework="4.0" batch="false" />
    ...
</system.web>

After compiling, you can change the value back to True or remove the "batch" attribute, and then rebuild successfully.

Had this numerous times. The solution is to close and open Visual Studio.

In my case at least it seemed to hove something to do wit