Sales Order not transferring to APO

Hello Experts,

I tried very hard to search the solution but couldn't get any answer for my query.

We have 4 Cust Orders in MD04. The three Cust Orders are transferred to APO and we can see them in RRP3.

There is one Sales Order that is not available in APO.

When I do CCR , I see the message -

"Sales Order Missing in APO "

Error Code - 236

Message no. /SAPAPO/CIF236

I checked Application Log  and found the error message as below:--

"Customer Requirement N BM 1001242823 000010 0001 : Schedule Line Already exists in SAP APO"

Not sure what to do to send this order to APO.

Regards,

Prabhat