When you go to Settings, connectivity, Internet Settings...do you have 'allow local connections' checked as 'yes'?...if not, that is most likely it...I am assuming you do not have a data plan, which is why you would get that error...the phone is still trying to connect using data coverage via your contract provider, and not your wifi connection...just having a wifi connection does not override that connection setting if it is checked as 'no'...
checking yes should allow the browser to default to the wifi connection when available...but you will need to do the same thing in the options of each application you plan to use also...
