dry, immature leather-look cherries

[joenix]

i have two small cherry trees in my garden. both self pollinators. one of them is doing well with big fat slightly reddening cherries. the other blossomed well, started to form fruit, then over about 2 weeks these fruits stopped maturing, shriveled up and dropped off.
the trees grow about 4 metres apart and i keep them well pruned. any ideas as to why? the same goes for my blueberries. one bush is doing wonderfully, the other two are shriveled and seem dead.
thanks in advance for any advice!
sarah