Taxonomy Theme set everything as "System Default"

Having had Taxonomy Theme module running successfully in my Drupal 5.1 install, I have in the last 48 hours been adding pages and finding that the Theme selection on a node add screen just shows "System Default" and gives no other choice. On noticing this I went to eht Taxonomy Theme admin screen and on the "By node type" screen all of the node type dropdowns have also gone to "System Default" and don't show any other alternatives. This is not completely broken as I can add pages via the Extended Paths screen but as you can imagine this is not ideal.

Any ideas of why this has happened and what I can do to get my themes back? Thanks.