I too had a problem opening the disktrays of my readynas. On netgear's forum there is the solution using a pin:
insert pin at "B", and move pin toward to buttom gently to release latch. This will move plastic block (colored in Cyan) behind front cover.(source: http://www.readynas.com/forum/viewtopic.php?f=20&t=5286)
After that I removed the harddisk from the tray and used a spray on the latch and so far it is better than before.
The spray I used was Instant Cleaner from Philips which is used to clean off fingerprints and so on from electronic equipment.