I have noticed that if you have a DWARF scene file, and you have imported new meshes or materials, and then take those items out of the DWARF folders & try to re-open the file (that was saved with the new objects used in scene), DWARF will hit a glitch looking for those objects (Njpaul mentioned this would be good to have a 'graceful' way of looking for missing files).
Make an entry in our bug tracker. You should be able to access it at http://www.projectwish.com/e107_plugins/bugtracker2/bugtracker2.php?0.bugs.1
Ah, right! Will do, Thanks Njpaul .