I started having the same issue again with one board I just bought (X10SLM+-F) with firmware 3.66. The other X10SLM+-F works fine with the same firmware version. The problem occurred on two different PCs and it's consistent: one board can be accessed from both PCS, the other cannot be accessed from any PC.
I tried several times to flash firmware again, reset to factory defaults, cold reset the IPMI/BNC, nothing worked ...
When I looked at the IPMI webpage I saw something weird on the Configuration -> SSL certificate. The board that didn't work had a SSL certificate valid from January 2018. Then I looked at the date in the BIOS ... it was 2014
.
As soon as I configured the date correctly in the BIOS and rebooted the PC, I could connect again (both from IPMIVIEW and by launching the Java console from the browser). Yeah
I remember reading that SSL configuration needs to take place before iKVM.exe starts. It was stated on Supermicro website.
The SSL certificate is stated to be valid only 3 years since it was generated. The strange thing is that the board that was working from the start has the correct date in BIOS but the SSL certificate expired. Go figure
So to sum it up, although the error seems to indicate an error on your client PC,
check your network IPMI/BNC configuration that you're in the right subnet especially, check the date in BIOS, check the SSL certificate date. I guess if you'r BIOS date is before the SSL certificate validity start date, you won't be able to connect.
Because the SSL certificate is only valid 3 years, check those settings again if this happens. I guess the conclusion is that it's not the actual BIOS update that screws up IPMI. Rather it's the clear CMOS process and lost of time reference that makes us unable to connect to KVM console.
Hope this helps somebody