Using Drush Site-Install in C#

I'm trying to do a Drupal site install using Drush in C# as part of a full Windows Server site installation using MSI. The Drush commmand I am using is the following one.

C:\ProgramData\Drush\Drush.bat -y si application_name --db-url=sqlsrv://admin_name:password(local)\SQLEXPRESS:/database_name --account-name=admin --account-mail=name@test.com --account-pass=Password1234 --site-mail="admin@company.com" --site-name="Site Name" install_configure_form.site_default_country=GB install_configure_form.date_default_timezone="Europe/London"

And this works perfectly when run from cmd.exe when in the working directory (inetpub\application_name).

The issue arises when the above is put into code and executed during an installation and always results in the following error (with a different file name each time).

Unable to decompress C:\ProgramData\Drush\lib\druFD63.tmp.gz

The C# code being used to execute the command is as follows:

public static ActionResult Drush_Configuration(Session session)
    {       
        string strArgs = "-y si application_name --db-url=sqlsrv://admin_name:password(local)\SQLEXPRESS:/database_name --account-name=admin --account-mail=name@test.com --account-pass=Password1234 --site-mail="admin@company.com" --site-name="Site Name" install_configure_form.site_default_country=GB install_configure_form.date_default_timezone="Europe/London";
        string strExeCmd = @"C:\ProgramData\Drush\Drush.bat ";
        strExeCmd = strExeCmd + strArgs;
        string strLocation = @"C:\inetpub\application_name";

        session.Log("Starting Drush Configuration");
        session.Log("Command line is: " + strExeCmd + " " + strArgs);

        int exitCode;
        ProcessStartInfo processInfo;
        Process process;
        try
        {
            processInfo = new ProcessStartInfo("cmd.exe", "/c " + strExeCmd);
            processInfo.WorkingDirectory = strLocation;
            processInfo.WindowStyle = ProcessWindowStyle.Normal;
            processInfo.CreateNoWindow = true;
            processInfo.UseShellExecute = false;
            // *** Redirect the output ***
            processInfo.RedirectStandardError = true;
            processInfo.RedirectStandardOutput = true;

            process = Process.Start(processInfo);
            process.WaitForExit();

            // *** Read the streams ***
            string output = process.StandardOutput.ReadToEnd();
            string error = process.StandardError.ReadToEnd();

            exitCode = process.ExitCode;

            session.Log("output>>" + (String.IsNullOrEmpty(output) ? "(none)" : output));
            session.Log("error>>" + (String.IsNullOrEmpty(error) ? "(none)" : error));
            session.Log("ExitCode: " + exitCode.ToString(), "ExecuteCommand");
            process.Close();
        }
        catch (Exception e)
        {
            session.Log("Error: " + e);
            return ActionResult.Failure;
        }

        session.Log("Drush Configuration completed successfully");
        return ActionResult.Success;
    }

And as stated above, this always results in the "unable to decompress" error.

Has anyone ever used c# to run Site-Install in Drush? Does anyone know why this might fail when executed in this way?

Any thoughts or advice would be greatly appreciated.

I am using Drush-5.8-2012-12-10-Installer-v1.0.20, Drupal 7, and Windows Server 2008 R2 x64.

The cause of this issue was the Environment Variables. The Drush MSI installer sets up User Path Environment Variables which are not recognized in an MSI machine context.
So, by adding System Path Variables for Drush, GnuWin32 and PHP to the site-install MSI the site can be programmatically installed.