I have just started having the same problem.
Was using Google Drive on iPad with no issues. Exited Google Drive and put iPad down for a few minutes to do something on my computer. Picked it up again and it had lost connection. Normally when this happens, I just tap my network in WiFi settings and it connects again, but this time the wifi symbol came up in the top left corner for about half a second before I got a blank page with some html at the top ( <HTML><HEAD><TITLE>Success</TITLE><HEAD><BODY>Success</BODY></HTML>, same as someone else had above), and then an error message over the top of it saying "Error Opening Page: Hotspot login cannot open the page because it is not connected to the internet". The page is the same apple Log In page that shows up when I have to connect to the network at uni (where I always have to enter my user name and password) but my home internet usually just connects automatically when I turn it on.
What I've tried so far:
1. Turning iPad off and on again
2. Turning my routers off and on again (unplugging them for 15 minutes and then plugging back in)
3. I've tried telling the iPad to forget the network. I've also tried resetting all network settings. No difference.
4. Other wireless devices including iPod, Nintendo 3DS, mobile phone all connect fine, it's just the iPad that has suddenly and randomly decided not to.
Has anyone found any solutions to this? I won't be at uni for a while and I have no other access to a wireless network to test it on another connection.
Also I tried using the Apple email support option, but they just sent me an email with a link, telling me to click the link from my device. Given my device can't connect to the internet (wifi model only) and therefore can't access email, this was pretty unhelpful.