It means that you have already created this ledger in tally and are trying to make it again
You may have created it in wrong head
What to do in this case?
Do not create ledger again
Select Ledger Already Created
If ledger not showing, it means you have created ledger in wrong head
How to Change or Alter Ledger Group already Created?
Accounts info --> Ledger --> Alter (ALA) --> Select Ledger --> Change Group --> Enter Enter or CTRL A