I had repeating wlan connection drops before 1.21 version. BUT I *think* it was a complex situation since there are multiple sources for drop outs: channel overlap in 2.4 GHz spectrum (only ch 6,11,20 or non-overlapping) causing errors, 5.2 GHz issues with thick walls etc; buggy WPA2 implementation (tkip part disturbs so use AES mode only); compatibility issues between Dlink stuff and Netgear as well as Intels WLAN h/w in computers etc. So... I clean up my environment and part of it was upgrading my DAPs to 1.21 fw. Now they have been stable and auto-connection seamlessly (I never check anything anymore, or just for the fun of it) for 1 month. So, yes my advice is:
-upgrade to fw 1.21 in the DAPs
-use non-overlapping channels in 2.4 GHz spectrum
-use 5.2 GHz for multimedia and when using the DAPs at bridges for wired equipment ie the DSM-510 or other media players
-Use WPA2 in AES mode only