I thought I'd pass this along, I received my GCs about 10 minutes after I ordered them yesterday but was not able to actually use them on the site. I kept getting that there was a problem entering them and tried off and on all day. Now, I use Linux and the Firefox browser so I booted up my Windows machine and tried that way, still using Firefox, it was a no go. I switched to the Internet Explorer browser and got right in and used my GCs to place my order with no problems, including the $15 coupon code.
I don't know if they worked the kinks out of the site or because I switched to IE browser that I was able to order, it might just be an activeX thing that only IE renders properly but it might be worth a try if you use Firefox. The other thing is that there are security measures built into IE that limit some activex activities so check your settings and give it another go.
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Equal opportunity annoyer