Import data from excel in ax2012 r3

Hi ,

I want to import data of two linked custom tables (header & line) using excel. Below points i should take care during import

1.one common field should not be mandatory.it should import data even if we dnt giv any value.

2.one field should set to default value.

I tried to import data but even if i click on publish button it is not doing any processing and data is not getting imported.