Problem on freereport and barcode

[superc]

Hello,
I'm try to using freereport for print a report that contains 3 string and one of these is a barcode Code128A;
if I enter in design mode in freereport and set a barcode with a specific string, (in my case 'LT12345' for example) I read code with no problem, otherwise if I pass the same string from memory table the generated barcode is not visually the same than before , and infact I don't read it....
WHYYYY?

Thanks in advance.