Help with error "...may be caused by a mismatch in the TLS version. ..."

Hello folks,

I am trying to connect to my work VPN server using FortiClient v. 5.6.2.1117 on Windows 10 x64, but every time I enter my username and password, it says "Warning - Failed to establish the VPN connection. This may be caused by a mismatch in the TLS version. Please check the TLS version settings in the Advanced of the Internet Options. (-5029)".

I have checked the Advanced panel under Internet Options, which has checkboxes for "Use SSL 3.0", "Use TLS 1.0", "Use TLS 1.1", and "Use TLS 1.2". When I first checked, the boxes for SSL 3.0 and TLS 1.0 were unchecked, and TLS 1.1 and TLS 1.2 were checked. I tried checking TLS 1.0 in addition to 1.1 and 1.2 and restarting my computer, but it still fails. I have tried several other combinations (like unchecking 1.1 and 1.2, so only 1.0 was checked, or checking only 1.1 or only 1.2, etc.) to no avail. I have also tried uninstalling and re-installing the FortiClient app with no success.

This started after my computer told me it needed to restart to finish installing some Windows updates, specifically KB4093112 (2018-04 Cumulative Update for Windows 10 Version 1709 for x64-based Systems). I had also just installed Visual Studio Build Tools 2017, in case that may be pertinent.

I am also emailing my workplace's computing services department in case they have seen this issue before, but any assistance would be much appreciated.

Best Regards,

Matt S.