Okay I have had my n900 since December, no issues with wifi until now. Only place the Wifi never worked properly was at a friends house, well it would connect but never load a page. But that didn't bother me as I could use 3G.
I believe my problem originated from having the kernel-power-settings installed. Everything was fine until a new update came in yesterday and completely screwed up the device. I was getting internal application error for the clock, and other apps when i wasn't even using them. I restarted the device, done cold boots, uninstalled kernel-settings and still made no difference.
I have since re-flashed the firmware as well the emmc. Everything is working fine apart from WiFi which keeps giving me the "Network Connection Error". My router is the same and it has always worked with ease. I have tried the suggestions on the forums here using the killall commands & rebooting the device but it doesn't make a difference.
Also ive not installed any apps or created any new repositories since ive flashed it, so its as new. All ive done is restore my contacts only (no settings, bookmarks, calenders etc). Only thing i have installed so far is Rootsh to use the commands posted here.


Can anyone please offer any other suggestions/advice.....?


Thanks

Do you use a Livebox or other router with built-in MAC filtering?

ive got a netgear dg834gt, but the problem isnt the router as i tried connecting to a router with no password on it and it wouldn't connect to that either. It used to work fine before.
I think that power-kernel-settings has perhaps left something resident behind somewhere. As that is why i flashed it, apps and device was crashing/restarting and wifi ceased working. Now everything is working apart from wifi.

thanks to all the unhelpful folk here, ive sorted it myself and its now working!