I was using three screens just fine, I was connected with two DVI cables and one mini DP to DVI adapter. At one point I also added a mini DP to VGA adapter and was running four screens.
I wanted to run the one that was on VGA at a higher res so I bought another mini DP to DVI connector, but I was unable to use it as I received the message saying 'The display settings could not be saved. Please try a different combination of display settings.'
So I decided to go back to how I was originally but I am no longer able to use three monitors, no matter which combination of DVI or mini DP to DVI I use.