Need to display error meesage for Tcode MD50, Any User exit???

Hi,

For Tcode MD50, We have to give the input sales order number and Sales Order Item number and press enter, It gives detail output for MRP.

Here After giving the input sales order number and Sales Order Item number , when we are pressing enter I need to display a error message at status bar based on sales order number.Is there any user exit or badi for the same?

Please help me. I am using ECC5.0 version