sql database exception error in c# asp.net

Question

Hi .I'm developing asp.net web application. i make sql database with table "reg".and actually i make 2 web forms for reg complete process.
  reg1.aspx has username,password,etc...
  reg2.aspx has dropdown securityQues.

actually table reg have 3 columns
                       1.username not null  2.password not null 3.securityQues not null

when i click reg1.aspx submit btn "sqldatabase exception by usercode" cmd.executenonquery(); error.. null values could add on table


 plz help for this prlm... sorry for mistakes in english help me adv.thanks for all members