Object of type 'System.Int32' cannot be converted to type 'System.Web.Security.Cryptography.Purpose'

I am getting this error now whenever I try to build. I just installed Visual Studio 2012 and .Net 4.5, but this project is still on 2010.

Here is the line of code I am having issues with:

private static MethodInfo _encode;
public static string Encode(CookieProtection cookieProtection, byte[] buf, int count)
{
  return (string)_encode.Invoke(null, new object[] { cookieProtection, buf, count });
}

I receive an ArgumentException was unhandled by user code error saying, "Object of type 'System.Int32' cannot be converted to type 'System.Web.Security.Cryptography.Purpose'" Nothing has changed in my dev environment and my co-workers are not having the same problem, but they also do not have VS2012.

I found an article about Sitecore having this error, but this is the only place I have seen it pop up.

There they say, "This is because in .NET 4.5 there are some new namespaces in System.Web "

Their solution is to:

• Uninstall VS11 if you have it installed
• Uninstall .NET 4.5
• Reinstall .NET 4

This seem like a ridiculous solution that 4.5 and 4 cant be on the same machine.

Does anyone know what may be causing this and any better solutions before I try to un-install and re-install a bunch of stuff?

A comment also says to try: </setting name="login.rememberlastloggedinusername" value="false" > but I don't want to do that either.