C# 2010 WebBrowser Control doesn't work on Win7-64 with 'Any CPU'

I created a new VS2010 C# WinForm project, .NET4, added a WebBrowser control with the following code when the form loads:

public Form1()
{
InitializeComponent();

string strPdfFile = @"C:\RK_ERP\quote\2014-02-014.pdf";
webBrowser1.Url = new Uri(strPdfFile);
}

Under the Build Tab, if I set the Platform Target: to x86 (That was the default), it works on Win7-32 & Win7-64 machines. If I set Platform Target to Any CPU, it only works on Win7-32. It won't display the PDF on the Win7-64 machines. I've tested on Win7-64 machines with IE 9&10 installed.

The Configuration Platform: is Active(x86). I can't change that for some reason.

This is being done in an effort to fix the same problem in a large ERP project. The retesting if I switch 'Platform Target' would be huge, so I'd like to avoid that. I'm developing currently on a Win7-32 machine.