Hi Partha,
First check the field in screen layout, has it been put as mandatory?
If yes , you have to maintain the value in this field. If you want to pur costant value in this field , you can do it in auto field mapping under rules for that field.
if this field is in recording and you donot want to put values in it , make this field as initial in auto field mapping under rules for this field.
Hope this would help you.
Regards
Pankaj