try change the select like this :
sql = "select CATEGORY , COUNT(CATEGORY)as CatStac from tblRentals where dateIssued > #" & MyStringDate1 & "# AND dateIssued < #" & MyStringDate2 & "# GROUP BY CATEGORY"
Add this to your code to bind your dataSet to chart :
'Set chart data source
chart1.DataSource = ds
'Set series members names for the X and Y values
chart1.Series("Series 1").XValueMember = "col1"
chart1.Series("Series 1").YValueMembers = "col2"
'Data bind to the selected data source
chart1.DataBind()