Taxonomy Title 6.x-1.2 gives a 500 error when the term is saved. This doesn't happen with Taxonomy Title 6.x-1.1.
I also have Nodewords enabled and I'm using Drupal 6.10.
Please try the new release. I can not recreate your problem but I suspect it is related to http://drupal.org/node/663630.
Should be a duplicate.
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