For anyone getting errors, please send me a copy of the dictionary file. I'd suggest the following process, to make sure that no personal data is contained in the file:

• Backup the dictionary: "mv /home/user/.osso/dictionaries/.personal.dictionary /home/user/.osso/dictionaries/.personal.dictionary.old"
• Kill hildon-input-method to clear the cache: "killall hildon-input-method"
• Launch the Notes application and type in a new word (any random set of characters should work fine)
• Retry AutoComplete Editor to make sure you still get an error
• Copy the new dictionary, which can now be safely sent to me: "mv /home/user/.osso/dictionaries/.personal.dictionary /home/user/MyDocs/failing_personal_dictionary
• Replace your original dictionary: "mv /home/user/.osso/dictionaries/.personal.dictionary.old /home/user/.osso/dictionaries/.personal.dictionary"
• Kill hildon-input-method again to clear the cached data: "killall hildon-input-method"

You can now send me (via email, PM, or attaching to a message here) the /home/user/MyDocs/failing_personal_dictionary file.