Question Launching an application as another user on a remote PC

[Thequazi]

The setup:
Two computers, one on a domain, and one not on a domain.
The computer that isn't on the domain has a folder with permissions for "Authenticated Users" (our domain administrators group).
The executable resides on the domain pc and is launched under an account not in the administrators group.
The target file resides on the non-domain pc. A drive is mapped to this PC (L
I prompt for the username and password, which I believe is being store properly, and invoke process.start. After passing it the information I always get the "Incorrect username or password" error.
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I've changed the domain from long form to short form with no success, even changed the domain to that non-domain pc and entered local admin creds with no success.
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I don't really know which direction to look from here.

    Public Function ConvertPWtoSecure(ByVal str As String)
        Dim password As New SecureString
        For Each c As Char In str.ToCharArray
            password.AppendChar(c)
        Next
        Return password
    End Function

    Public Sub LaunchTargetEXE()
        Dim username As String = TextBox1.Text
        Dim password As SecureString = ConvertPWtoSecure(MaskedTextBox1.Text)
        Dim domain As String = "longform.domain.com"
        Dim filename As String = "L:\targetfolder\target.exe"
        Try
            System.Diagnostics.Process.Start(filename, username, password, domain)
        Catch ex As Exception
            Throw ex
        End Try
    End Sub