error in Get Receipt Lines - cannot close because the system is currently working

Hi, somebody encountered the same error in Purchase Invoce, Get Receipt Lines when i click OK error msg Purch. Receipt Lines cannot close because the system is currently working pops-up.

Then when i click OK error msg You must not specify Work center No. in Purch. Recpt. Line appears (Document No and Line No. given)

This error appears on just selected POs only.

Please Help! Much thanks in advance

Are the PO’s existing in Purchase Line table or deleted?