Purchase order in 'Archived' status

Hi All,

We are using SRM5.0 ECS.

After SC is created for 'Free text' requirement, PO is created. When looking at the Purchase order in 'Process Purchase orders',it is giving the message as 'Error while reading the PO in backend system, Inform system administration'. When looked into Item details it is showing the status of PO as 'Archived'.

This is happening only for random Purchase orders. Please let me know what could be the issue.

Regards