AFAIK AEM Forms is a standalone product that you can use in your own
environment. The other marketing cloud products (such as Analytics,
Target, etc.) are not needed for AEM Form. However, integration will
other marketing cloud products will provide additional enhancement to
AEM Form should you need it later.
If the issue is happening on every folder in DAM, I would suggest trying
to recompile all the JSP pages . If not, there might be an issue with
the content within the folder. I would check the validity of each asset
in the folder. http://localhost:4502/system/console/slingjsp
If none of these possibilities could explain why you got the SNFE, I
would recommend opening a ticket with the support team to assist
further. If you have a reproducible scenario, it would be even better.