grirdview and paging

hi for all
i have page show my employee  data 10/pages ;this grid have data from data table
Q1:why when i  press on page2 error return. it's tell "The GridView 'GridView1' fired event PageIndexChanging which wasn't handled. "
Q2: how can make next page on button out grid  for example 
             sn   empname     
              1         a
 <<        2         b          >>
              3         c
          ...