Hello Majd rami,
Sounds like; you were performing manual reconciliation with a bank account but now you are changing it to set for advanced bank reconciliation process.
Before doing that; please check first in Unreconciled transactions form in this bank and what are the transactions are still not reconciled.

After that, check in Account reconciliation form if there is any new line / lines are created for reconciliation purpose. If created; then check in Transactions form, what are the lines already marked to reconcile.


Now you can do the following.
--- In Transactions form; first remove the tick marks from the lines which are already marked to reconcile.

--- Then delete the line itself.

Point to be noted: - Make sure there should not be any transactions available in the "Unreconciled transactions" form for this bank before you are trying to enable the Advanced bank reconciliation check box. If still any posted transactions available; then please reconcile them first.
Kindly check and provide your feedback.
Best regards,
Sourav Dam
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