Visual Studio 2010 "System.Web" reference unresolved [C#]
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I'm having trouble with adding a reference to my project. I need the `System.Web` reference in order for my code to work but the reference won't stick. When I look in the Solution Explorer, I found this alert icon on top of the reference I added. I have the same reference in another project within the same solution and it is working fine.

![The reference that has an alert icon on it][1]


If you look at the properties of this reference, you'll see that the `Resolved` attribute is set to `False`

![The properties of this reference][2]

Does anyone know how I can fix this or what's causing this problem?

  [1]: http://i.stack.imgur.com/GJqyB.png
  [2]: http://i.stack.imgur.com/hYWMh.png