Hi Kashif,
First read the error message carefully, the reason for the error is mentioned in it.
The problem is that,the Internal table 'ITAB_HEADER' there is no field called "LTEXT" , but is there similar fields: "PLTXT", "TEXT1 is there. You have to correct the fieldname in the program or declare a field in the internal table called 'LTEXT'.
Regards
Jeffin