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Error code 0x204 can occur when trying to connect to a Windows computer from a Mac using the Remote Desktop protocol. One of the most common causes of this error is when the Remote Desktop Protocol is not enabled on the Windows machine you are trying to access.
You can fix this issue by enabling the Remote Desktop Protocol manually via the System Properties screen on the Windows machine and by allowing Network Level connections. You may also need to configure your firewall to allow Remote Desktop connections.
In some cases, antivirus software can cause the 0x204 error code when using Remote Desktop on a Mac. Certain antivirus apps could interpret remote connection attempts as unauthorized users with malicious intentions.
It should be noted that this is an English QA forum, and Korean is recommended to go to the corresponding Korean support forum.