FWIW, their own service manual basically states to keep trying until you get it to "take".

one of those potential infinite loops if you look at the process flow.

Yeah I noticed that as well on the dealer documentation. So I'm clinging onto the hope that it might work eventually if I keep trying. I tried several times last night before calling it quits, and then again this morning. Still no luck, but... Hope I get lucky.

New Key Worked!
 

I bought a key blank and transmitter online via ebay (seller: midwestkeyless), and got it cut this afternoon. Had both good keys with me, so I tried to code the key and it worked like a champ. It looks like either the keys can either go bad, or there's certain ones that will work with late 03 and early 04 build RX8s. The first blank I had cut was actually from the dealer, and that will not work at all. I didn't get to see the P/N of the key, but the service tech left me with the impression that they were all the same.

In anycase I just wanted to pass along my experience in case someone else runs into the same situation as I had. I'm switchblade Pimp Status now. :D:

Same guys I went through. Glad you got it straightened out.

Congrats! I wish I hade problem with the key coding, my remote still wont program and I dont know what rremote would work with my car.

Thanks! I seemed to be the odd one out with mine. I had problems with the key instead of the remote.

What FCC ID and IC does it list on your new flip key? The flip key that seems to work for early build US spec cars are:

FCC ID: KPU41788
IC: 4238A-41525
Visteon No. 41524

For reference, my original FOB had this info:

FCC ID: KPU41805
IC: 4238A-12076
Visteon No. 41848

If it's true that US spec cars PCM won't work with EU, maybe they're the same as the ones for Japan and can use one that was made there?

Yeah, something like that.
The Flip key I ordered were
kpu41788
4238a-41525 visteon. 41525

Didn't work at all, And I dont think the other remotes u mentioned would work either.
Did you have the same visteon number on your old fob as the flip key?

My old fob has the visteon 41844. No FCC ID, No IC.

Dude, I finally got myself a working flipkey. I bought one from UK and it worked perfectly with the programming this time. The US remotes has another freq. thats why it didnt work in the first place. But I notice that the battery inside the fob is weak, how do I change the battery? I searched, but I only found when they explain how to separate the key from the fob.