Wifi not working on 8900

Hi guys, wondering if anyone can help me with my 8900.
I have had to send my phone back for repair and they have replaced it with a new phone.
I have tried to set up my new phone with WIFI, which i had before (and it worked) but i'm getting the message FAILED TO AUTHENTICATE AGAINST THE NETWORK.:confused:
Does anyone know what this means, its driving me mad.
Blackberry internet is so slow so prefer to use wifi.

Any help would be great

Thanks Sarah :)

That will happen if there is a security problem with the wireless router.

The simplest way to check it out is to disable security, leaving the router Open. You should be able to make a default connection.

Once you are connected, re-apply the security setting and try it again.