I suspect that the generated workbooks do not register in the Running Object Table that's why the code doesn't find them .
Can you load the server generated workbook(s) , run the following ListAllBooks routine and post here what output you get in the Immediate Window ? This should give us a snapshot of the situation.
Author: Jaafar Tribak Link: https://www.mrexcel.com/board/threads/how-to-target-instances-of-excel.1118789/page-2#post-5395519