In a standard Motif XmFileSelectionDialog widget,

inside the XmNokCallback procedure, if the code decides that the selected file
is not acceptable, what is the correct procedure to either force the file
selection dialog to stay up, or redisplay the dialog ?

The dialog is defined as an unmanaged XmFileSelectionDialog in the UIL file.
The code that triggers the dialog is inside a callback (when user does a
File->Open) and does a simple XtManageChild(open_dialog_widget).

However, in the XmNokCallback, if I try to XtManageChild of the
open_dialog_widget, nothing happens

What is the correct way, from within the XmNokCallback procedure to either
cause the dialog to stay up where it was, or have it completely wind down and
redisplay from scratch ?

(Ideally, I want to pop an error dialog on top to provide explanation why file
is unacceptable).