Honda Civic check engine light?

We bought my sister a used 2002 Honda Civic a couple weeks ago, and she loves it, but it didn't have a way to hook her iPhone into the radio. In my Trailblazer I have a cassette player where I put this little Cassette to iPhone adapter. She only has the factory AM/FM CD Player. I went on eBay and found a remote cassette player (a cassette player that plugs into the back of the factory radio and mounts where the storage bin is located under the radio). I purchased it as a Christmas gift, and installed it this weekend because she is out of town and I wanted to surprise her with it. Before I removed the radio I disconnected the battery, when I finished and put everything back together I reconnected the Battery and did all of the tests on the radio, like putting in the code, etc. And then I turned it on to park it where she had it and the check engine light is on! It was not on before I started. So I get the code reader and it says P1259: Vtec System Circuit Fault (Bank 1). What does that mean? It runs normally accept when it switches from 2nd gear to 3rd and 3rd gear to 4th it revs really loudly in between the switches (automatic).It has done that since like a week after we bought it. I'm getting worried about this car, I thought it was great, an 02 Honda with only 117000 miles, and now this only like 3 weeks after we buy it. Any help as to which parts I should replace to fix this would be great!

Added (1). I did not get the AUX adapter like you are speaking of because I'm 16 and I have to buy gifts for other people too and my summer job did not pay that well and it is $60 and the cassette player was only $25 and it sounds just as good. But I'm not asking if the cassette add on was better than an aux adapter, I'm asking if installing the radio could have thrown the code (which we have established didn't) and what I can do to fix the code. I'm also not looking for someone to be condescending and tell me how impossible it is to answer this question. If you lack the ability to answer this question, then please don't. Two people have given me input, which proves that while this is a tricky question, you could have just as easily recommended I see a mechanic without being condescending.

Are you a mechanic? No? Then go find one. No one can guess long distance as to a car's issues. Not possible. It is hard enough with training and tools and experience to find the issue. Go find a mechanic.

It has nothing to do with the radio.

Just a coincidence.

It sounds like your Vtec System has failed or has a bad connection.

And you would have been much better adding an actual AUX input adapter to the stereo rather than a cassette player.

http://enfigcarstereo.com/HON_AUX_DMX_V1.html
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