PS2 Disc Format error?

I recently bought Sims: Bustin' Out for my PS2 and played it once but it froze before even starting the whole game and after restarting it, the disc wouldn't read. All my other CD's work perfectly fine but this one wouldn't work. It only says "Please insert PS2 format disc". What should I do? What is wrong? I've tried cleaning the disc with disc cleaner, alcohol, tap water and peroxide but it still wouldn't work. I'm about to resort to opening the PS2 and wiping the laser if that helps. But I'd like to know why that happens.