Help please, all coupons just stopped working all of a sudden

I've just been made aware by a customer that discount codes are not working.

I've gone back through the order records and the last time someone used a discount code was on 11/25/2009, I guess coupons stopped working after that.

Does anyone know if there's a reason why all coupons would stop working all of a sudden? Is there a settings that disables all of them?

The coupons are currently listed active and have an expiration date of late 2010.
I've been using the same coupons without making any changes since 2006 and they just stopped working all of a sudden.

What does it tell you when you enter the coupon code? Any error message? Can you add a new coupon that works?

If you want help you have to provide more input.

I'm having the exact same problem.
When trying to use a coupon code it says that the code is not valid for any products in the cart.
The problem seems to only be for coupon codes with restrictions.

If they worked before and they are not working now, then something has changed - What version of Zen Cart? Any recent addons installed? Has your server upgraded php or MYSQL? Exactly what settings are you using on the coupons?

Version 1.3.8a
No recent add-ons
I don't think my server has upgraded anything but I'll find out.
Coupon settings:
Amount 20%
minimum order 0.00
uses per coupon blank
uses per customer 1
start date 1 December 2009
end date 1 January 2010
coupon zone restriction none

No category restrictions (couldn't get them to work)
two product restrictions

url: https://www.twiddletails.com/store

Sorry for not being more specific before, I think my problem is the same or very similar to that of twiddletails

I'm running ZC 1.3.7 on this particular shop, I also get the message that says the code is not valid for any products in the cart.

I actually also run 4 other shops on the same server (2 with 1.3.7 and 2 with 1.3.8)
All shops also have the same set up with discount codes, and I have not changed this since 2006. All coupons have the restriction not to apply to a 'specials' category.

Coupons are working just fine on all the other 4 shops, but I don't why they stopped working on this one all of a sudden. I haven't made any changes

The 'specials' category is inactive, don't know if that has anything to do with it, but then again it's been inactive since about half a year ago and coupons stopped working less than a month ago.

If I create a coupon without any restrictions it will work, but I'd like to use some coupons with some restrictions.

For anyone with this or similar problem, I applied the bug fix listed here and it seems to be working now: http://www.zen-cart.com/forum/showthread.php?t=138711

I still don't know why coupons stopped working all of a sudden when I didn't make any changes and have been working for years like this before. I have other shops with the exact same settings and coupons are still working on those.

Thank you so much for following up and posting that link. Save me a lot of digging. :D