I would have check the following on the host router before updating:
What wireless modes are you using? Under Setup/Wireless/Manual.
Try single mode G or mixed G and N?
Channel Width set for Auto 20/40Mhz or try 20Mhz only.
Try setting a manual channel to a open or unused channel.
What security mode are you using? Preferred security is WPA-Personal. WPA2/AES Only. Some WiFi adapters don't support AES, so you might want to try TPIK only or Auto.
Any cordless house phones?
Any other WiFi routers in the area? Use
InSSIDer to find out.
Turn off Short GI, WLAN Partition and Extra Wireless Protection if you have it. Under Advanced/Advanced Wireless.
Can you do a factory reset on the DAP and check the operation of the connection type and see if it operates correctly? What FW version did you have prior to upgrading?