Table control - error message

Hi,

I am having Material and serial number in the table control.Material is in enable mode and serial number in

disable mode.After entering material number I am checking whether it is serialized or not,if it is serialized I am enabling serial number field so that user can enter serial number(IN pbo).After entering the

serial number,the serial number field disabling automatically,my problme is that I need to check whether

the Material number and serial number combo already exists,if it is alrerady exists I need to raise the error message and also user able to change the serial number field(but it is disable after user entering the value).