vb.net - ASP.NET Downloading files from an SQL table -

i'm trying download file sql server table. using gridview. whenever try download file, corrupted file.

i using asp.net , vb.net sql server 2012 express.

any ideas why ?

protected sub gridview1_selectedindexchanged(sender object, e eventargs) handles gridview1.selectedindexchanged      dim contentid = convert.toint32(gridview1.selectedrow.cells(1).text)     dim contentname = gridview1.selectedrow.cells(2).text     dim contenttype = gridview1.selectedrow.cells(3).text      lblcontentname.text = "[ " + contentname + " ]"     lblcontentname.visible = true   end sub  protected sub gridview1_rowcommand(sender object, e gridviewcommandeventargs)       dim cn new sqlconnection("data source=brian-pc\sqlexpress;initial catalog=master_db;integrated security=true;")      if e.commandname = "download"         dim filename string = string.empty         dim id integer = convert.toint32(e.commandargument)         dim cmd new sqlcommand("select content_name,content_type,content_data content content_id = " & id, cn)         cn.open()         dim dr sqldatareader = cmd.executereader         dim bytes byte()         dr = cmd.executereader()         if dr.read()             filename = dr("content_name").tostring()             response.contenttype = dr("content_type").tostring()             response.addheader("content-disposition", "attachment;filename=" & filename)             bytes = directcast(dr("content_file"), byte())             response.cache.setcacheability(httpcacheability.nocache)             response.binarywrite(bytes)             response.flush()             response.[end]()         end if     end if end sub  private sub bindgrid()     dim constr string = configurationmanager.connectionstrings("connstringdb1").connectionstring     using con new sqlconnection(constr)         using cmd new sqlcommand()             cmd.commandtext = "select content_id, content_name content"             cmd.connection = con             con.open()             gridview1.datasource = cmd.executereader()             gridview1.databind()             con.close()         end using     end using  end sub   protected sub page_load(sender object, e eventargs) handles me.load         if not ispostback             bindgrid()         end if     end sub