TL;DR

Go to PO > Reports > Setup > Advanced

Then read the Report file field

Details

To locate the Report file from the ASP Page

First, go to Purchase Orders in MC, select any PO associated with the issue, then move over to the Reports tab.

From the reports tab, select Set up a pop-up, which will display, and in the Advanced Tab, will show the "Report File" as an ASP file.