I'm trying to run a process as a different user that has Administrator privilege in 2 different computers running Vista and their UAC enabled but in one of them I get a Win32Exception that says "The directory name is invalid"

Can anyone tell me what is wrong with my code?

var myFile = "D:\\SomeFolder\\MyExecutable.exe";
var workingFolder = "D:\\SomeFolder";
var pInfo = new System.Diagnostics.ProcessStartInfo();
pInfo.FileName = myFile;
pInfo.WorkingDirectory = workingFolder;
pInfo.Arguments = myArgs;
pInfo.LoadUserProfile = true;
pInfo.UseShellExecute = false;
pInfo.UserName = {UserAccount};
pInfo.Password = {SecureStringPassword};
pInfo.Domain = ".";

System.Diagnostics.Process.Start(pInfo);

UPDATE

The application that executes the above code has requireAdministrator execution level. I even set the working folder to "Path.GetDirectoryName(myFile)" and "New System.IO.FileInfo(myFile).DirectoryName"