I was able to fix the problem using NetExtender version 7.0.203, downloaded from mysonicwall.com.  This was the only version (back to 5.0.?) that was successfully able to connect to our TZ105, with a Win10 laptop with all updates.  Hope this helps someone else, I was just about pulling my hair out...
Hi, Our office has a SonicWall TZ105, with most recent firmware, and now with Windows 10, we are unable to connect via SSL-VPN.  The user name and password are correct, and I can connect with the Android app.  But in Windows 10, I have tried the MobileConnect App, most recent NetExtender from mysonicwall, used the terminal to create the VPN connection, and just manually made a VPN connection, and nothing works.   The president of our company just got a new laptop, and it has Windows 10, and I'm hitting a wall everywhere, but need to get her connected to our office.   Other VPN connections to other VPN servers work on that laptop, just not to our office.  It used to work with the same router settings on Windows 7. Every different method of trying to connect is giving a different error.  The strangest to me is "The specified port is already open."  But there are no other connections to that port, and am still able to connect using my phone.   Any ideas??  Thanks in advance!!
SSL-VPN Unable to Connect - Windows 10