Created Unassigned: MaskedEditValidator source code not found [27527]

I am attempting to use the MaskedEditValidator, when the page is rendered I get the following null reference exception.

Here is the call stack: AjaxControlToolkit.DLL!AjaxControlToolkit.MaskedEditValidator.OnPreRender(Sytem.EventArgs e = {System.EventArgs}) Line 360 + 0x29 bytes

I get a no source available screen with messages that indicates that it can't find the source code. I'm thinking that I must have installed something incorrectly.

I tried to install the Net40 binary for VS 2010.