next_post_link() not working

Hi, I am having trouble getting next_post_link() to work. I am using WP 2.2.2.

According to the Codex entry, WP 2.2 uses ‘1, 5, 15’ for excluded categories.

Tried that and got the MySQL error mentioned here.

Tried excluding categories this way: ‘1 and 5 and 15’ and there was no MySQL error, yet the links didn’t show up.

These are the different versions of the next_post_link() tag that I tried out:
<?php next_post_link(‘%link’, ‘Next post in category’, FALSE, ‘2, 8’); ?>
<?php next_post_link(‘%link’, ‘Next post in category’, FALSE, ‘2,8’); ?>
<?php next_post_link(‘%link’, ‘Next post in category’, FALSE, ‘2 and 8’); ?>

…none of which work out the way it should.

Any help please? Thanks!