HTC Desire :: Connected To WiFi Network But No Data?

I've had my desire for around a month now & had no real problems with it, flashed it with a stock ROM initially & then rooted it a couple of days after the root was released. When I woke up this morning I was connected to my WiFi network but when I tried to load a webpage, nothing happens, it comes up with the stock 'Web page not available' page. I tried a couple of web pages but got the same response, I thought it might be my WiFi network but when I got to work, exactly the same thing happens. I can connect via GPRS when I disable the WiFi with no problem. I've been using Y5 Battery Saver for the past two weeks, not sure if that's relevant. Is this a standard error / known bug, how would I go about fixing this, not having WiFi is obviously a bit of pain!

OK, installed a Terminal emulator over 3G & ran a couple of commands, including dmesg. From the output of dmesg it looks like the WiFi connects but then something goes wrong, here's a brief transcript:
pfn: set ssid = ******
Link event
Link UP
Enter set packet filter
start to add pkt filter 101
wds: 0021 @ 01
qmi: wds: network stopped
rmnet_stop()
wds: 0022 @ ff
qmi: wds: DISCONNECTED
If this is any use, I'm happy to try other commands.