>No, nMarks is between 2 and 20 at the time of the error--but the timestamps on the Word templates on the client's server do not have the dates I expected. I'll restore those from backup and test again.
>
>Update: You were right, as usual :-) The client had modified their templates in such a manner that the bookmarks were not properly formatted. The count of bookmarks returned 0.

You should add check nMarks=0 and display warning that template is invalid.