The most simple and stupid solution is to just wait 24h, and then SCCM will let you remove it 🙂
If you want it fast, you can try this:
Open your regedit:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\SMS_SITE_COMPONENT_MANAGER\Component Servers
Find out your old DP, and on each “Deinstallation Start Time” REG_DWORD value to 1.. then restart SMS_SITE_COMPONENT_MANAGER.
However, if the old DP already no longer accessible, you can directly remove it from SQL database:
Here is the ultimate way to remove a DP from SCCM:
use CM_<sitecode>
declare @ServerName varchar(15)
set @ServerName=’<orphanFQDN>‘delete from statusmessages where machinename=@ServerName
delete from Summarizer_Components where MachineName like ‘%’+@ServerName+’%’
delete from summarizer_sitesystem where sitesystem like ‘%’+@ServerName+’%’
delete from statusmessageinsstrs where insstrvalue like ‘%’+@ServerName+’%’
delete from sysreslist where servername=@ServerName
delete from sc_sysresuse where nalpath like ‘%’+@ServerName+’%’