We use the Cisco IPSec VPN Client to connect to our ASA for VPN access. Most users have little problem connecting, no matter what ISP they use. The exception is Verizon Internet users, particularly FIOS users. For these users we have to clear the "Enable Transparent Tunneling" checkbox on the transport tab and the connection usually works.
The real problem we have is with the Verizon 4G MiFi 4510. When these users launch Cisco IPSec client they are able to connect to the VPN but they cannot access any internal network resources. The client shows that they are connected, but they cannot ping, RDP, open network shares or use Intranet sites.
I have tested this on the same computer using the MiFi side by side with my personal home network. I can connect to the VPN gateway from both networks, but I can only see internal network resources using my home network. When not using the Cisco VPN client both networks allow me to get to the Internet just fine.
I have confirmed that the MiFi is on the latest firmware revision. I'm using the Cisco IPSec VPN client version 5.0.07.0290 thirty-two bit client. The "Enable transparent tunneling" checkbox is cleared in the connection configuration. Our PC platform is still Windows XP SP3 with latest service packs applied.