Hi,
Hi,
There may be some different reasons to cause the issue,following link for your reference:
The CA server's FQDN was actually not resolving in DNS.
https://social.technet.microsoft.com/Forums/windowsserver/en-US/361e4784-770b-4ac7-93ef-a8260d95fa6c/problem-with-adcs-web-enrollment?forum=winserversecurity
Security and Access Permissions for local and remote.
https://social.technet.microsoft.com/Forums/en-US/09f4bbc4-fa83-424c-850d-dbb48cbb8c2c/ccertrequestsubmit-the-rpc-server-is-unavailable-0x800706ba-win32-1722?forum=winserversecurity
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Best Regards,