Executing a program from an .ashx

I'm trying to start a program on the web server with an .ashx using the
System.Diagnostics.Process.Start(startInfo) function. It works when I'm
debugging in VS2008 but doesn't work when running in a production mode.
Obviously, I have a permissions issue since it's running under the
restricted permissions of the web user but I don't know how to allow it.
I've tried setting the user name, password, and domain of the
ProcessStartInfo object with the administrator's logon information (just to
get the highest permissions for test) but it tells me I have a bad user name
or password. I am concerned that I'm not setting the password correctly
because I'm using:

SecureString password = new SecureString();
password.AppendChar('p');
password.AppendChar('a');
password.AppendChar('s');
password.AppendChar('s');
etc.

Any examples of how to do this.

Thanks,

sr