I have had similar errors to this one on multiple configuration options in the group policy editor.
When I am trying to add an outbound firewall rule (block outgoing UDP 17500) under:
(Computer configuration > Policies > Windows Settings > Security Settings > Windows Firewall with Advanced Security > Windows Firewall with Advanced Security - LDAP://CN...)
It results in the following error:
Which from what it appears, the actual firewall rule itself is parsed correctly, however I cannot find anyone else having this particular error on the internet dealing with adding GPO configurations.
The closest I've found is that there might be a replication error between DC's however there is only one DC in the environment.
Anyone else run into this before?