Shopping Cart error 'Document Currently Locked' while approving

Hello,

Can anyone help me to resolve below issue in production environment,

An approver is trying to approve the SC then getting message as "Document currently locked" hence he could not able to approve the SC.

I have cheked the Table: BBP_WFLOCK but not found any lock entries also no lock entries in SM12

So, what could be the root cause and solution?

Regards,

Venkat