Set Focus On Particular Control When Opening Child Form

We have a main form which opens an MDI child form. What we want is to set the focus on a particular control in the child form, namely a telerik textbox. When the form is opened for the first time, the focus is set to the textbox control which has a tabIndex = 1 as expected. If the winodw is closed (and disposed) and then reopened via a button on the tool bar that calls the same code that opens the window when the application starts, no control has focus. We have added lines such as Me.rtxtPatientId.Focus() in the Paint event, load event, and activated event handlers but still cannot get the focus to the control. The code is quite extensive so posting it is difficult. However, here is the section that opens the child window:

if PatientSearchForm Is Nothing Then
PatientSearchForm = New frmPatientLookup
End If
PatientSearchForm.MdiParent = Me
PatientSearchForm.Show()
If PatientSearchForm.WindowState = FormWindowState.Minimized Then
PatientSearchForm.WindowState = FormWindowState.Normal
End If
PatientSearchForm.Activate()
PatientSearchForm.rtxtPatientID.Focus()