404 on the mason dhandler for /Ticket/Attachment

My RT install is working pretty well, with a couple small exceptions.

One is that I can’t download any attachments.

If I click any attachment link, I get a 404 error.

If I go to the Ticket/Attachment dir, and copy dhandler to xxx.html
and then call /Ticket/Attachment/xxx.html, I get the
expected "Corrupted Attachment URL, but at least I know xxx.html
is getting executed.

It’s like the dhandler isn’t getting called at all.

Any ideas? I’m not even sure were to start, or if there’s
some setting I can set in Mason that would do a better
job of reporting what may be wrong.