Car stereo question

[pergau]

My Kenwood stereo died the other day so I bought a Sony cdx-gt200. My choice was limited because I wanted a stereo that did Long Wave and I fancied an Ipod connector.

I installed it using the ISO connector that I had for the old stereo but when I turn on the sony, I get an error message that indicates that the speakers or amplifier aren't connected properly yet it works perfectly.

I have double-checked the wiring and it appears to by correct and I don't have an amplifier.

Am I missing something? or do you have any ideas?