To follow up, too much salt also causes problems, but less severe ones... or rather ones that time can fix. Too much salt kills off the bacteria very rapidly, and decelerates the rate of proteolysis through rennet. So you have a lot of peptidase quickly, and not enough of the right kind of proteins to break down. End result is poor or very very slow flavor development. Also, depending on your salt schedule and ageing process, you may get other faults, like crumbly texture or low moisture.
I think the sweet spot for cheddars is about 1.5-2% salt, IIRC.
It's amazing how every little detail in cheesemaking is important.