I changed my WLAN channel from channel 6 to 3 and that allowed my N900 to catch my WiFi for 2 days without a problem.

Yesterday night same issue again, I could connect to my neighbors unprotected WLAN but not to mine's.

I changed the WLAN channel again, this time from 3 to 4 and the N900 was able to connect to my WLAN afterward.

It would be good to know what causes the deadlock to happen