Iphone 4s, IOS 7.1.2 problem with charger wire this accessory may not be supported?

HOw to fix this problem

But some days ago it worked without any problem but now i don't know why suddenly it shows this msg.

It "MAY not be supported" but chances are that it is. If it works to do what you want, then keep on using it. If not, replace it with a certified cable.

You need an Apple certificated cable (MFI certification: Made For iDevices).
If you are using an USB extension cable, remove it.