Can you try logging in as admin and see if the problem resolves (assuming this is on a lower level env, which it should be since you installed ACS Tools)403 indicates you may have some login or permissing problems.Thanks

The use of doHandle404() should be abstracted away from you in the ACS Commons provided 404 overlay [1] which you shouldnt be changing.You should only have a /apps/sling/servlet/errorhandler/404.jsp that includes the ACS Commons provided 404.jsp (per the instructions).Can you check to make sure that...

Note, this issue was further investigated @ https://github.com/Adobe-Consulting-Services/acs-aem-tools/issues/122 ...The sample CSV file uploaded to the GitHub ticket works on AEM 6+ when uploaded on a Mac. This may be a Windows issue?

Checkout the ACS AEM Commons Error Page Handler [1] .. its a robust mechanism that allows for Authors (or site owners) to define authorable Error pages in AEM 5 with just "normal" CQ pages.You can also checkout the source code on the GitHub Project to see how its built out and/or get inspired on how...