Cannot upload images

Hi, I get this message when trying to upload pics.. any idea how to fix it?

Many thanks for your help,

WordPress database error: [Unknown column ‘none’ in ‘field list’]
INSERT INTO wp_post2cat (post_id, category_id) VALUES (2055, none)

Warning: Cannot modify header information – headers already sent by (output started at /mysite/wp-includes/wp-db.php:121) in /mysite/wp-includes/pluggable.php on line 275