Some users unable to post - time between posts error

[Deceiver]

G'day,

I recently upgraded our forum from 4.x to 5.5.3 (now 5.5.4 Patch 1), which went well, but I've had a user PM me claiming he's unable to post.
Sure enough, after logging in as this user, I too am unable to post. The error we get is:

This forum requires that you wait 15 seconds between posts. Please try again in 574109905 seconds.

For those playing at home, that's a touch over 18 years.

I've tried manually editing this user's profile to change the last activity and last post dates to hopefully reset this, but no avail.

Any suggestions on where and what I might need to edit in the database to alleviate this?

Thanks.

[Wayne Luke]

You can try a query:

UPDATE `user` SET `lastpost`=UNIX_TIMESTAMP(NOW()) WHERE `userid`=XXXX;

Should allow them to post after 15 seconds.

[Deceiver]

That did the trick. Thanks Wayne Luke