Why nlapiSubmitField() not works everytime? I am trying to update some values on long type field, it's working for few fields and not working for few one.. how this can be possible? Is this Defect? That Netsuite don't want to tell us??????/

code?

Depends. Could be you're trying to update a dynamic field.

Related to what Felipe says, some fields can not be updated via submitField(). The records browser tries to indicate which ones (though I don't think it's entirely accurate)