"A common cause of this sort of problem is that the BYOND pager is unable to reach the hub to verify your account. You need to configure your firewalls to allow byond.exe, dreamseeker.exe, and dreamdaemon.exe to have full access to the Internet.

Also, it is common for a firewall to have options for allowing only a certain version of the program to have access, which it does by using a hash such as MD5 to make sure the program hasn't changed. If an option like that is in use, it is strongly recommended to turn that off for these three programs. Many times, after a BYOND upgrade a firewall ends up mistakenly blocking the newer version for this reason." ^{Lummox JR [link]}

In the rare case that this should not be the reason, please read these instructions completely.

Did you make completely sure that there is no firewall (maybe a hidden one that you aren't even ware of) with hash/version checking blocking BYOND?

This seems to be the only reasonable explanation as to why you suddenly encounter problems after an update, as you said you went through the other instructions.