I think that I need to communicate my experience:
1. SD Card alone works fine.
2. 2xDS18B20 + 1xDHT22 works fine.
3. SD Card + 2xDS18B20 + 1xDHT22 ; only DHT22 works!
But, I had the system few days ago that had been working with 2xDS18B20 + SD Card? Now, I can't re-produce the working condition!
I have been investigating the situation. I suspect that it could also be the power problem -- an issue that has been thought in Post#1.