How can I prevent Access Denied errors with System.Diagnostics.Process.Start

My WPF app allows users to add "a开发者_JAVA百科ttachments" (Word, Excel, Text documents etc). The app generates Access Denied errors as it attempts to open a file on our company network. The error occurs after Process.Start is executed. The shell application opens (i.e. Notepad for a text file) then the "Access Denied" message appears. Initially I had similar errors attempting to write files but I fixed that problem using the Impersonator class found here.

Here is the problem code:

using (Impersonator impersonator = new Impersonator())
{
    System.Diagnostics.Process process = new System.Diagnostics.Process();
    process.StartInfo.FileName = pathToDocument;
    process.StartInfo.UseShellExecute = true;
    process.Start();
}

I get the same error doing this:

using (Impersonator impersonator = new Impersonator())
{
    System.Diagnostics.Process process = new System.Diagnostics.Process();
    process.StartInfo.FileName = pathToDocument;
    process.StartInfo.UserName = "uid";
    process.StartInfo.Domain = "domain";
    process.StartInfo.Password = new System.Security.SecureString();
    foreach (Char c in "password")
    {
        process.StartInfo.Password.AppendChar(c);
    }
    process.StartInfo.UseShellExecute = false;
    process.Start();
}

The deployed app fails even when I hard code my own user id and password (I have "full control" permissions to read, write, execute etc). Everything works fine if I change the document path to be a different shared drive that has relaxed security (where everyone is granted full control). The app is deployed with basic ClickOnce settings. The app is not installed on the users machine - it is available online only. What should I do to prevent Access Denied errors?

Thanks in advance.