2-factor Authentication with FortiToken

Hi all,

since a few months we use 2-factor authentication with FortiToken (Mobile and Hardware) for some Firewall-Policys, which works like a charm. Now we decided, to use the same authentication for a dialup IPSec VPN on the same Fortigate. Basically it works with FortiClient 5.2.4, but some users are unable to use a tokencode older than 15 seconds! For example, when you open the app (FortiToken Mobile) and the current token is valid for the next 30 seconds, no VPN-connetion is possible. So you have to wait 30 seconds until the next token is showing and then login is smoothly. Any ideas? Thank you...