Validation of edit field control

Hello;

I'm using a CXTPControlEdit derived class with a masked edit control to input timestamps.
The user should be able to insert the timestamp and before loosing focus (tabbing to next field) the input should be validated and when validation fails not loose the focus.

I tried to resolve this by writing my own CTimeScaleEdit::OnKillFocus() method.
This methode looks like

void CTimeScaleEdit::OnKillFocus()
{
   CString strText=GetEditText();
   COleDateTime dt;
   // Try to parse the string
   if (!dt.ParseDateTime(strText))
   {
      MessageBeep(0xFFFFFFFF);
      // If this fails 
      GetEditCtrl()->SetFocus();
      return;
   }
   else
   {
      // Reformat the string to be shown as expected
      CString strBuffer;
      GetTimestampFormatted(dt, strBuffer.GetBuffer(128), 128);
      strBuffer.ReleaseBuffer();
      SetEditText(strBuffer);
   }
   CXTPControlEdit::OnKillFocus();
}

When trying this solution the behavior is soewhat undefined because when the vaidation fails once, return keys won't be handled anymore.

What am I doing wrong? Whats the best way to handle edit control validation in command bars?

Thanx in advance

Martin