When adding a vCenter server to virtual machine manager you might encounter the error “Could not retrieve a certificate from the FQDN server because of the error: The underlying connection was closed: An unexpected error occurred on a send.”
The root cause is a TLS incompatibility. The VMM server cannot connect using older TLS protocols and ciphers. To fix, make the following reg changes after taking a full backup of course:
$NetRegistryPath = “HKLM:\SOFTWARE\Microsoft\.NETFramework\v4.0.30319”
New-ItemProperty -Path $NetRegistryPath -Name “SchUseStrongCrypto” -Value “1” -PropertyType DWORD -Force | Out-Null
$NetRegistryPath = “HKLM:\SOFTWARE\WOW6432Node\Microsoft\.NETFramework\v4.0.30319”
New-ItemProperty -Path $NetRegistryPath -Name “SchUseStrongCrypto” -Value “1” -PropertyType DWORD -Force | Out-Null
Then restart the virtual machine manager server. You should now be able to add the vCenter server. Other errors could be related to missing updates. The latest vCenter versions are only supported with 2019 Update rollup 2 or later.