Because some hardware manufacturers build in sftwarer inhibitors that won;t recognised what are in effect illegal copies of copyright material.
The music industry has bleated long and loud about the 'infringement of trevenues' caused by copying - as far back as the days of cassette recordsers, there were dark mutterings about all new cassette recorder / players playing non-commercial tapes with a loud hum to ruin the enjoyment of anyone naughty enough to tape an album they already own to play in the car.
That was all swept aside by the arrival of CD's and copying software, but the advent of the MP3 / filesharing revolution has left the music mogusl floundering. They ever saw it coming, and are still playing catch-up - and this is a rather tedious, mealy-mouthed example of their petty penny-pinching attitudes to people who by and large by original copies of albums anyway.
You could either renplace your player, or get an MP3 adapter and plug your i-Pod in - that'll show 'em!