Ok, on your website when image information (name, description, keywords) has a word that present more then once, and one of these words has a capital letter, it produces this error.
For example a name "Проба проба" will cause the error.
I believe it has something to do with MySQL configuration rather then PHP/Apache/4images
Unfortunately I still can't reproduce this error on my local server.
Try execute this mysql query in phpmyadmin:
INSERT INTO 4images_wordmatch (image_id, word_id, name_match, desc_match, keys_match) SELECT DISTINCT 636, word_id, 1, 0, 0 FROM 4images_wordlist WHERE word_text = 'ïðîáà'
will it give you error?