Hi,
>>We had a long time ago removed an old DC and haven't added any additional domains until recently and everything seems ok until
now.
After demoting the DC, please using
ntdsutil.exe to clean up the metadata in case unexpected issues occurred.
From how to use this tool and clean up dirty data, please refer to link below:
https://technet.microsoft.com/en-us/library/cc816907%28v=ws.10%29.aspx?f=255&MSPPError=-2147217396
>>"The trust relationship between the primary domain and the trusted domain failed"
Please open the cmd console on your DC, type domain then press enter, open "AD domain and trust console", right-click your domain name, selected properties,trusts-> verify that your old DC has not been there, and click
properties for other trusts, click validate button.
>>Can I remove this without any issues?
Ntdsutil will automatically help you with them, if not, please manually clean up it.
Best regards,
Andy
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