Get a process owner username...

I really need some help on this one.

I need to get the owner (domain/username) of a process.  I found some code
on CodeProject <http://www.codeproject.com/KB/cs/processownersid.aspx> that
looked/looks promising for what I need but it still falls short.
I can't seem to get past the OpenProcessToken Win32 api call that I need.

Here's some sample code that I'm using just to test it out:

public enum DesireAccess : uint {
    STANDARD_RIGHTS_REQUIRED = 0x000F0000,
    STANDARD_RIGHTS_READ = 0x00020000,
    TOKEN_ASSIGN_PRIMARY = 0x0001,
    TOKEN_DUPLICATE = 0x0002,
    TOKEN_IMPERSONATE = 0x0004,
    TOKEN_QUERY = 0x0008,
    TOKEN_QUERY_SOURCE = 0x0010,
    TOKEN_ADJUST_PRIVILEGES = 0x0020,
    TOKEN_ADJUST_GROUPS = 0x0040,
    TOKEN_ADJUST_DEFAULT = 0x0080,
    TOKEN_ADJUST_SESSIONID = 0x0100,
    TOKEN_READ = (STANDARD_RIGHTS_READ | TOKEN_QUERY),
    TOKEN_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED | TOKEN_ASSIGN_PRIMARY |
        TOKEN_DUPLICATE | TOKEN_IMPERSONATE | TOKEN_QUERY |
TOKEN_QUERY_SOURCE |
        TOKEN_ADJUST_PRIVILEGES | TOKEN_ADJUST_GROUPS | TOKEN_ADJUST_DEFAULT
|
        TOKEN_ADJUST_SESSIONID)
}

public static string GetProcessUser(Process p) {
    IntPtr k = IntPtr.Zero;
    var t = OpenProcessToken(p.Handle, DesireAccess.TOKEN_ALL_ACCESS, out
k);
    var lastError = Marshal.GetLastWin32Error();
    var exception = new Win32Exception(lastError);
    return null;
}

When I step through this bit of code the OpenProcessToken method returns 0.
According to MSDN<http://msdn.microsoft.com/en-us/library/aa379295(VS.85).aspx>a
return value of 0 indicates an error.  So I use the
Marshall.GetLastWin32Error() method and then create a new Win32Exception
object to retrieve the message.  The message is Access Denied.
I'm at a loss to understand why that error and what I'm doing wrong here.

Any suggestions?

Thanks,
Mike

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