Jiggerypokery

I have a Radio Shack cassette adaptor which I would like to use in my WRX03 standard stereo so that I can use my iPod in the car.

This adaptor takes the form of a cassette and a 3.5mm jack plug for those who don't know what I'm talking about.
Either my wife or I managed to get this to work last year, but I recently tried it again with no success, it just won't stay in (auto eject) no matter what way round the tape is, which direction it's playing etc.

Now, has anyone else had any difficulty getting a cassette adaptor to work in this car, and if yours works perfectly - which make is it?

I don't want to buy another one if it's a common problem, the adaptor works fine in my other stereos.
Thank you.