When you promote a DC in a multi DC environment wan connectivity or other issues may prevent the server from becoming a DC as it fails to replicate the sysvol folder.
If you want to force replication from another DC you can stop ntfrs edit the below registry key that the KCC automatically populates to enable replication from an alternate source. Â Afterwards restart ntfrs.
net stop ntfrs
regedit
2003 Server
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTFRS\Parameters\SysVol\DomainName
2008 Server
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTFRS\Parameters\SysVol Seeding\Domain system Volume (SYSVOL Share)
Edit the key Replica Set Parent to point to the server you want to replicate from
net start ntfrs