[Zope] all dtml rendering as source after 2.4 upgrade (heelp)

This is bizarre.. upgraded from 2.3.x to 2.4.2. Zope seems to be running fine except that all DTML is shown in source mode - my own methods, the ZMI etc. Purged and reinstalled a clean zope 2.4, fired it up again with my old data.fs, same thing. Anyone got any ideas why this could happen or how to fix ? Short of downgrade, export, upgrade, import ? Thanks in advance, -Simon