I've tried searching for help with this in Cisco's support community and Google and couldn't find much...
Essentially I connect to our guest wireless with my iPod Touch and I then get redirected to the Cisco Landing page asking for a user name and password, which are created, stored, and managed on the Guest Controller. When I try to type in the user name and password, the text boxes never fill with what I press on the onscreen iPod keyboard. If I type the correct user name and password I have and hit enter I do not authenticate.
This used to work just fine but all of the sudden it no longer works. I tried with a laptop and things are fine. I know the controllers were updated recently to version 6.x and the Guest Controller appears to be on a 4.2.x version, but I wouldn't think this would be the issue as Guest Wireless still works fine for everyone and everything else.
I've never setup the scenario you described because normally the guest controller is on the same code version, becasue prior to 6.x.x.x code it wouldn't work unless they were all the same code revision, but there was a bug in the 4.1/4.2 code that related to the meta-refresh tag, that caused some clients (99.5% worked fine and never had issues) to behave irratically sort of like what your describing, this issue could possibly be more prominent with the fact that the interior controllers are on 6.x code and the Anchor is on 4.1/4.2 code.
Maybe this info will be useful.
The only time I have seen that issue is when we used a custom Web-Auth page and certain html code that the iphone, itouch did not seem to recognize. If you are using the default Cisco Web-Auth page, then I don't know what the issue can be. 99% of my installs are cutome web-auth pages and one of my test is to make sure the iphone works. So far the only issue I had was with certain html coding.