A previously fine iPrint server has now taken to throwing up 500 errors
when I try to add printers from maptool. Existing printers work fine,
users can install, view etc without any problems. However, clicking on
the little magnifying glass icon and selecting the broker gives the 500
Internal Server error.

The server is a NetWare 6.5 SP5 box, with the same version of broker,
IPPSRVR.NLM and NDPSM that's been running fine on this and other servers
for months. IPP DEBUG screens show nothing useful. Where can I start to
troubleshoot this one?