are you doing "url-redirect" from ACS by any chance? I've noticed before that it will not work if WLC is configured as "RADIUS (Cisco Airespace)" in ACS. Once I changed to "RADIUS (Cisco Aironet)", it started to work. Not a good fix, since "RADIUS (Cisco Airespace)" is required to support Airespace AAA parameters. :(
Please make sure that you're web browser doesn't isn't set up to use a proxy server.
Also I remember one scenario where I got the web authentication (splash screen) working with Mozill firefox but I couldn't get it to work with Internet Explorer. I called Cisco TAC and they had me type in a command. The Web Auth splash screen did come up after this command was configured on the WLC. Unfortunately I can't remember the command. You can try giving Cisco TAC a call and see what you can find our.
Transferring Crash file from standby: Login to the Active WLC in HA.
From CLI: (Cisco Controller) >transfer upload datatype crash (Cisco
Controller) >transfer upload filename (Cisco
Controller) >transfer upload mode tftp (Cisco Controller) >transfer
This is the start of a display filter cross reference between Wireshark
and OmniPeek. The 1st installment is a table of advanced filters. More
filters will be added as time allows. It is a living doc, so check back
for changes every so often Please feel f...