I don't think this is a problem with the Intel 520 SSD. SATA III 6GB/S interfaces were released on later Macs which surfaced around 2011.
Perhaps you should have checked your system information to see what SATA intereface you had before buying a new SSD.
That feels a little bit rough Rodney!
Sata is backward compatible, so if your machine is capable of sata2 speeds at 3 gig then putting a sata3 ssd in a machine to future proof it for a year or so seems reasonable?
I have this issue as well and it feels like the MBP doesn't like the sata3 into its controller.
I'll do some more digging but I haven't found much out there to help with this.
The intel toolbox when booted from DVD doesn't recognise the intel drive as being in the machine. I'd love to fix that as well.
Ok, I'm sorry if what I said sounded a bit rough, but when buying new hardware you really should look to see how compatible it really is with your current system.
Everyone knows that this industry is moving forwards very quickly and technology does not take prisoners when new parts are released.
If you are in doubt about system compatibility do not do it, unless you are prepared to take a loss. It is better to do your homework on the hardware, firmware and software that you'll be using rather than take shots in the dark.
The problem is the link speed negotiation between the SSD Sand Force controller and the MBP Nvidia controller. This is something that is recognized and acted upon by other SSD device manufacturers such as OCZ but there seems to be no way to get the 520 SSD working at 3Gbps in the Nvidia controller MBP's right now. OCZ have a firmware tool that (besides being an infinitely better solution than the half-ok Intel Win-tool and completely crap non-Win tool) that lets you force the link speed of the SSD device to 3 Gbps.
I recently tried out an Intel 520 SSD but will switch back to OCZ as they have much better support for non-Intel hardware (and other OS's than Windows - Intels focus on Win is weird - Linux and OSX users are people Intel can ill afford to not serve).