Hello John,
I think your upgraded copy of Moodle still has some old directories that existed in Moodle 1.4 but should not exist in Moodle 1.5. This could happen for example if you just copied the new version over the old version. For this particular problem you should delete the mod/quiz/format/qti subdirectory of your moodle directory.
Quiz
New quiz module code in Moodle 1.5 alpha
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