The virtual network adapter driver (Fortinet Virtual Ethernet Adapter) from 2018 is incompatible with Microsoft’s latest kernel updates. Fix: Run the VPN in “Compatibility Mode” for Windows 8. If that fails, you need a newer client.
Modern FortiGate firmware (7.x) requires TLS 1.2 with stronger ciphers that 5.6.6 does not support. Fix: If your FortiGate is newer than version 6.2.3, do not use this client. You must upgrade your FortiGate or downgrade the client. Forticlient 5.6.6 Download
FortiClient 5.6.6 remains a critical version for many organizations managing legacy systems or specific compatibility requirements within the Fortinet ecosystem. This endpoint security suite provides essential features like SSL and IPsec VPN, antivirus protection, and web filtering. Where to Download FortiClient 5.6.6 Forticlient 5.6.6 Download