I purchased a blank key from bay and had it cut locally. I then tried to program the key myself. I was able to use the included information and program the keyless functions without a problem. I wasn't able to program the immobilizer part to start the car. After trying for hours, I finialy gave up. I had a dealer try and they said it couldn't program to the car. They asked were I got te key, and said I needed to buy a Lexus key. I thought "ok" you just don't want to do it unless I buy your key. I wasn't to happy. I then tried for my local shop to try it. They cleared all the keys and programed my original master key no problem, then tried the key they had cut for me. They said it wouldn't work either. To my frustration I contacted the seller of the key and they resent new internal guts, the immobilizer part. I replaced the guts and tried again. To my amazement it worked the first time. The car started! Woo hoo!!!!

 

Considering the significant price difference between the Lexus OEM keys and the eBay keys, the eBay keys are worth the additional occasional headaches!

(I've used both)

 

I'm thinking this is my problem as well. After successfully programming the key only the remote worked and not the immobilizer. When I purchased my 03 car back in 2010 I only received the master and valet. So I purchased one (transponder only no remote buttons) off eBay and had it cut and programmed like a master key in case the only master key we had was lost. That put in my possession three working keys (1 master with remote keys, 1 master without remote keys, and one valet key). One would assume that there are five keys programmed in the cars ECU (3 in my possession and two in former owners possession (actually lost possession!). With my thinking there were no more allowable entries into the ECU. So I deleted all keys from the system except master key. After successfully deleting the other two keys that were working prior to that I still couldn't get my new remote key to start the car. Tried and tried. Gave up and went to bed as sooooo many have responded they did as well. So tonight I thought lets try programming one of the keys I deleted the night before to validate the methodology. Bingo. It worked. Programmed the second key I deleted last night as well. So now I'm thinking it is going to work with my new remote key. Wrong!! Which is why I'm thinking the guts are either the wrong ones or simply bad.
Disclaimer: I've read almost the entire threads concerning key programming and tried like four different procedures to no avail.

Is there anything else I can do besides contact the eBay seller (which I did late tonight) that might work? Thanks.