I've bought a Conceptronic C300BRS4A Wifi N compatible

Since that day I have noticed some Wifi connection issues. Although iphone still show Wifi connection working, with the IP and everything looks OK, when I try to connect with Safari, Facebook, Cydia, Mail ... I can't

So, I put Wifi off, and the on and start working again

I have iphone 3GS FW 4.3.2 and I never have been that kind of problems.

I'm trying to change some router settings:
* Fixed IP (sometimes I have DNS conflits)
* Change security WPA2-PSK to Mixed WPA2-PSK/WPA-PSK

I think the problem could be Channel BandWidth 20/40, but I want to use Wifi N for other devices.

Any idea what could be the problem?