Did you measure for acid while making the cheddar? If not, you might have made an acidic cheese. If the pH falls to low (typically below 5.0), the cheese will be somewhat dry, crumbly, and lacking in complex flavor. Also, the melting properties will be severely diminished. Basically, it will resemble Feta cheese.
What makes this especially frustrating is the fact that the cheese seems to be on target during the cheesemaking process. Without a pH meter, there is no way to know until you cut it open, or sample the cheese with a trier.