The key on a router like CSR is syntax. I had the same problem as all of you and read all of the same threads but nothing was clear about what the problem was.. missing route attributes, duplicate interfaces...
I found my configs firsts using
Router#show running-config | section app-hosting
!this showed my botched settings for the appid guestshell
>I used a 'no' command in front of each line I didn't want to clean up the config parameters
Router#no app-vnic gateway0 ! removes the gateway0 configs
you need to has an 'app-default-gateway (IP address) guest-interface 0'
also use 1 not 0 for the gateway as well as vnic NOT app-vnic
router(config-if)#vnic gateway 1virtualportgroup 0 guest-interface 0
router(config- gateway)#guest-ipaddress (IP) netmask (subnet)
see the pic attached