What's Wrong with this DHT22?
Two things:


You need to put a delay in between your read requests. Currently you're reading way too fast, every few milliseconds you're hitting the DHT. Max interval should be every two seconds or so. 
Add a 10k resistor between pin 1 and 2 of the DHT. 


I'd bet adding a delay, or using the simpleTimer library to control how frequently you read from the DHT will clear this up.