I remember this happening when we first started, but can't remember exactly what simple thing we did to fix it! Try turning off "Enable captive portal/Web authentication" on the network you ultimately want the users' DPSKs to be working on. I suspect we then had 2 WLANS set up - one as described above and another which issued the DPSKs for that WLAN.
I wonder initially if we were trying to distribute AND run DPSKs off the same WLAN?
Oh dear, it was two years ago and my memory is so bad....