why I setting font smoothing failure with CMsRdpClientShell?

my code is here:

CMsRdpClientShell m_MsRdpClientShell = m_rdp.get_MsRdpClientShell();

VARIANT font_val;
font_val.vt = VT_BOOL;
font_val.lVal = TRUE;
m_MsRdpClientShell.SetRdpProperty(_T("allow font smoothing"), font_val);