Open task in General ledger

I've three errors in Open task, which are showing these messages :

1. Only one ItemAccountingCodingBlockDistribution.ROOT permitted. The system detected an error situation which prevents automatic processing in the accounting process component.

2.Create not possible; source object does not exist. The system detected an error situation which prevents automatic processing in the accounting process component.

3.Cannot find account determination group for product category xxxxx

I understand that for third case we need to define an account determination group. But I'm not able to understand first two business transactions.

Please advice.

Thank you.

Regards,

Aruna Thakar