SSL VPN wont allow users to login after upgrade

Hi

Have a 3240C firewall, I have upgraded one from 5.2.7 -> 5.2.9 -> 5.4.4 and everything is working fine apart from the SSL VPN.  The Forticlient gets to 80% then fails with the message "Your username or password may not be configured properly for this connection (-12)". When it was on ver 5.2.7 the VPN worked fine, I have checked the settings and the release notes but can't find any info that might help.  I have even recreated the VPN following the admin guide with no luck.

Another 3240c running v5.2.7 is running the SSL VPN without any problems and using the same AD group and settings.

Any ideas or pointers as to what it could be?

Thanks

Ian