Account 12221001 requires trading partner to be filled

Hi

The user had some old documents and he is trying to clear them.

During clearing he is facing an error "Account 12221001 requires trading partner to be filled"

Trading partner field is blank in the reconciliation account 12221001 and also customer account.

BSEG of the document which gives the problem. The reconciliation account is 12221001, the trading partner for the customer line is not filled in.

How can we fill the trading partner on this line item?

Thanks in Advance,

Deepthi.