Unable to change Web Login Settings due to error on Cisco 5520 WLC

[Mogwai]

Please disable the WLANs using global Web-Auth/Web-Passthrough before changing Web policy.

That is the error that I'm getting when attempting to change the "Web Auth. Type" on the Security > Web Auth > Web Login Page.  I'm attempting to change the "Web Auth. Type" from internal to external. 

The WLAN in question is already disabled under the WLANs tab. 

Anyone have any ideas on how to remedy this?

Thanks

[Mark Elsen]

 - Not  a direct reply but worth looking into if you are on an older release :
                       https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-tac-recommended-aireos.html

 M.