I have the same problem... it used to connect without a problem out of the box... I have updated to OS 08 and my 810 just cant connect at all.

it states "Internet connection failed. Unable to retrieve IP address from server. Try again?"

if I tried to disconnect, it wont... wifi signal just keep blinking
close the browser, and turn off 810... boot it again... then launch "connectivity settings..." go to advanced go to IP Addresses tab insert IP address, subnet mask, default gateway, primary dns, and secondary dns address...

then it will state network connection error... but it shows there is internet connection but browser doesnt load anything

If the problem turned up when you switched to '08, and your previous version was a reasonably old version of '07, then it sounds like the problem is power saving mode. For the problematic connection, save the setting, then edit it and turn off power savings mode. Then test again.

I recently own my N810, and I have exactly the same problem: can't connect in open network points, where I can connect with my laptop, my Ipaq phone, and with a Archos 604 wifi too with any problems. I'm not a technician and I'm new in the Maemo world. Because of that I need some help to fix this problem in a practical and explained manner. Anybody can help me?????. Another detail: the only place where I can connect to an open whifi point is in my home where I have a Linksys router connected to an adsl modem.

I ended up bringing my laptop to all the open APs that I normally visit to find out what the IP settings are. Then I specified the IP settings for each network connection on the NIT - guessing at the specific IP. I chose a number high enough to make conflicts unlikely.

I will try to visit the Aps, and find the IP settings. Anybody can explain me why I can connect with my Lynksys in my home with any problem without introduce any data in the settings???

Must be something cached somewhere...
On my N800 I have also once in a while with public hotspots that I get "network connection error".
It was always after a initial successful connection to that network. If it then drops out, then sometimes reconnecting is no go.
Even reboot won't fix it. Connecting to other non-protected hotspots (after getting the error) gives the same error.
When coming home it however then connected always to my own wifi (WPA).
The next day I can then connect again to the public hotspot that had the problem (until the next time I get a "network connection error" ... but that is not always - works fine in most cases)
Did not managed to reproduce it, aldo I have the feeling that enabling blue tooth "helps" in provoking this problem...

Some older access points don't support the power saving protocol used by the N810. FON routers don't. Having a lower signal power and a busy access point seem to affect the ability to connect. I never have a problem with my home AP or those in Starbucks. For $7.95 a month I have a Boingo Wifi account for the N810 that includes roaming with AT&T. Also works at most hotels and airports in addition to McDonalds -- I don't do fast food but they're there is Starbucks isn't.

I just saw this in a other thread.

snip: "BT & WLAN on nxx0 share the same antenna as well as same RF amplifier."

Might be also helped by BT on... Maybe some routers don't like this "switching"...

I'll had the problem a few day's ago and it went away by both disabling BT and set for that connection the power saving to "off" (connectivity settings - connections - choose connection - edit last page "advanced" button - 3the tab" )