Does anybody knows what could be causing this?

The more info you share about your gear the easier it would be to give some advice, but just as a sheer guess I would say maybe the ohm rating on your speakers doesn't match your receiver.

check your connections. You may have some crossed wires.

Its a JVC HTIB.The first few days it played with no problems then it started saying its overloading.This is actually not my gear its my cousins.I havent been back to his house since we set it up.But he called me and thats what he told me.

1) Crappy speaker wire... Check it, the entire run, it could be exposed, bare, crossed, etc.

2) Check the ohm ratings on the speakers.

I'm betting that it's #1.

Also make sure it is not totally encolsed, overheating can also cause a reciever to overload.

He may have accidently hooked two speakers up to the same output.

Update it ended up being the speaker wire connections.When we hooked it up we were in a rush because I had to go to work.Rewired it everything works fine.Thanks for all the input.