VPN clients cannot connect (-12 error)

[ZuidnatieNV]

Hi all,

Since a few days our VPN clients are getting the following error when trying to connect: "Unable to logon to the server.  Your user name or password may not be configured properly for this connection (-12)."

Most of the FortiClient versions are v5.6.6, and our firewalls are running FortiOS v6.2.4.  We tought the error could be related to the OS of the firewalls, but we sometimes get errors on more recent client versions as well.

In some cases, Forticlient v5.6.6 could successfully connect again, when the QoS Packet Scheduler was disabled in the network interface properties.  Strangely enough, I never had issues with an older FortiClient running on a Mac.

Any ideas/thoughts on how we can tackle this error?  Thanks for feedback!