Just a few questions...
Do you have AD deployed in your company? (i know, stupid question. Just to be sure)
Is the QlikView server integrated into the domain?
Are those big shots member of the same domain?
If not, does a trust relationship exist between the two different domains?
Are the big shots accessing the access point from inside the company network (instead of from their iPad on an external wireless network - no SSO there, sorry)?
Are you using IIS as a web server and has IWA been enabled?