Thank you very much, Mark...but then, the wrong thing may be in the VI where I write data into the file. It could be that I don't get to save data correctly and so, nothing is saved and file is empty. Could you give me some idea of what could I be doing wrong?.... I'm quite new at LabVIEW)I'm trying to save different data types (arrays, double, cluster). Do I have to group the items of the same type together to save them?...