向Access数据库添加记录的问题。我实在不明白这么写究竟错在何处？

sub btnAdd_click(sender as object,e as eventargs)
dim provider,SQL,ConnStr as string
provider="Microsoft.Jet.OLEDB.4.0;"
ConnStr = "Provider="+Provider+"Data Source="+Server.MapPath( "/db/SupplyersInfo.mdb" )+";Persist Security Info=False;User ID=;Jet OLEDB:Database password=123"
SQL="select * from supplyers"
dim objConnection as oledbConnection=new oledbConnection(ConnStr)
objConnection.open()
dim cmd as OledbDataAdapter
cmd=new oledbdataadapter(SQL,ConnStr)
cmd.selectcommand=new oledbcommand(sql,objConnection)
dim ds as dataset=new dataset()
cmd.fill(ds, "supplyers")
dim dr as datarow=ds.tables("supplyers").newrow()
dr.item("aaa")＝MatType.selectedItem.text
dr("b")=MatSerial.text
dr("e")=MatName.text
dr("c")=Mat.text
dr("d")=MatSpec.text
dr("f")=MatModel.text
ds.tables("supplyers").rows.add(dr)
cmd.Update(DS, "supplyers")
end sub
运行后总是出错说“Update requires a valid InsertCommand when passed DataRow collection with new rows”，cmd.Update(DS, "supplyers")这行颜色为红色指明是这行有问题。
高手请指教一下究竟错在哪？感激不尽