Help!! trying to execute a process from a program executed from Registry Run Key

Sorry, I wasn´t clear, let me be more specific.
My real problem is how to execute a program and let it run on a diferent user than the logged user, I´ve create a Local User account with administrative rights and over this account I want to let my program run. Then i wrote a program that shuld execute the other that I want to run over a diferent account, the account that I´ve told before. This first program(the one that execute the real program) is execute at windows start, to do that I put in windows registry in Run key the direction of the first-one, this first-one is execute at windows start but it throw an error when it tryes to execute the real program over a diferent account than the logged-one, the code seems like that:

try
{
Process proc = new Process();
proc.StartInfo.FileName = "programdir";
proc.StartInfo.UseShellExecute = false;
proc.StartInfo.UserName = "localAdministratorUser";
proc.StartInfor.Password = GetPass();
proc.Start();
}
catch(Exception e){e.Message();}

The error message is: Invalid directory name
But the directory name is fine, if I just execute by clicking this first .exe, it execute the 2nd very well over the account that I´m specifying in the code. It´s realy crazy to me.

Yes, I'm using the full path (c:\windows\file.exe) for example, I've checked it out.Even I've used it explicity It seems really extrange to me, it just doesn't work.... sorry my English please.