Most people reporting this error are running the AnyWhere Access on Essentials 2016, or possibly 2012, for the first time. However, I have run into this twice in the past few months, rerunning the wizard to renew the public access SSL certificate on older Essentials 2016 servers. Perhaps this is caused by a recent update. Many report waiting a while resolves the issue, but I have not found this to be true.
100% credit for the solution goes to JVH Consulting https://jvhconsulting.com/2022/01/02/2016-essentials-anywhere-access-setup-fails/
JVH advise you need to add 2 registry entries to each of 4 registry keys. NOTE: if you are not familiar with doing so, editing the registry incorrectly can destroy your server. As always, back up the registry before starting.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v2.0.50727]
“SystemDefaultTlsVersions”=dword:00000001
“SchUseStrongCrypto”=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\.NETFramework\v4.0.30319]
“SystemDefaultTlsVersions”=dword:00000001
“SchUseStrongCrypto”=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\.NETFramework\v2.0.50727]
“SystemDefaultTlsVersions”=dword:00000001
“SchUseStrongCrypto”=dword:00000001
[HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319]
“SystemDefaultTlsVersions”=dword:00000001
“SchUseStrongCrypto”=dword:00000001
JVH suggest a reboot may be necessary, but I found simply restarting the Essentials Console was sufficient.