IPhone: Charging is not supported with this accessory What does it means?

image Here there's a screenshot I took.

I don't know what does it mean, is it dangerous for my phone, or something?

It means that it can't charge using that charger. Duh. I mean really?

Its not dangerous, it just means that it isn't going to charge it. Usually its because the ihome or whatever you were using for it is older than the iphone or ipod. My ipod was the newer one and I had an older Ihome and now it doesn't charge with it.