Problem while raising an error message

Hi,

I written some code in one BADI, PROCESS_ITEM method. This is for doing some validations in ME23n transaction. If i put a deletion indicator for any line item, it should show an error message there itself, depending upon my requirement. But error is coming while saving. i need that error message there itself, immediately. Can you please help me....

Thanks in Advance.

Siva Sankar.