Since when is SL account a free account?
First my SL account didn't get any character slots and now I found that characters on that account can't be org leaders.
Character I tried to promote is not "free player" and promoter is org leader so org leadership should just transfer over.You can only promote someone to one rank-level below your own level (The exception is the leader, who - when a new leader is appointed through promotion - will lose the leadership). Free players can not be organization leaders.
Type '/org ranks' to list the ranks of your hierarchy.
Your rank is President.