Oct 19, 2015 03:37 AM|Angie xu - MSFT|LINK
attempting to leverage DirectoryServices to call DirectoryEntry.invoke("SetPassword") in what i would consider a fairly common sense. Unfortunately I have run into a total stop when the invoke returns a "RPC server is unavailable" exception.
Perhaps the account for Internet Information Services (IIS_IUSRS) did not have permissions to SET Passwords for Active directory.
Please check whether you have similar issue like this:
Cannot set password with DirectoryEntry.Invoke when user is created in AD
hope it helps.