I know that last weekend a conversion using this tool on tens of thousands of subrecords went off without a hitch.

Do you have more than one link between the parent database and the sub database? The simple reparent tool only works if there is a single natural link.

Well, I removed the relational subform but that did not correct it.  Some more digging and I found that the Parent form had multiple "subform" type fields listed in the Tree Branch to Manage a Database.  Instead of only one, I had about 4 fields listed with the Type of SUBFORM.  So, I deleted them all, and removed all subforms from the Parent form.

I then created a new subform with natural links.  Made sure that name of the subform field matched the exact spelling of an existing subform field name.  Opened the subform, looked for orphans and found four of them.  Did Reparent process, saw nothing happening.  Checked again for orphans, and found none.  Then opened the Parent form, and found 4 records on the subform for the child, exactly as expected.

So, problem solved.  I suspect it was because of old subform type fields in the Parent form.  (Could these have been the result of some earlier XML import problems)?    

Suggestion:  Provide some type of status message when the Reparenting process has been completed.  Similar to the mesage when orphans are found, something like this:  "4 records have been reparented".

This is a major improvement for use when importing data into subforms.   
Thanks again, keep up the good work.