SSL VPN Stuck Status 40% v7.0.0.0029

Hi

When I use the FortiClient SSL VPN v7.0.0.0029 it gets stuck at 40% whilst connecting, it then gives a -5 error. If I use client 6.4 it works, my problem is 6.4 doesn't install anymore due to an invalid digital signature. Any help would be much appreciated.

Thanks