VHDL error - natural type does not match string literal

Hi,

I am trying to make a simple program which will turn on the green LED when the Key(0) is pressed and when we leave the key, it will be switched off.

I am getting this error in the code for some reason though -

Error (10515): VHDL type mismatch error at pract.vhd(36): natural type does not match string literal

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.numeric_std.all;

use ieee.std_logic_unsigned.all;

entity pract is

port (

iKEY : in std_logic_vector(0 downto 0);

oLEDG: out std_logic_vector(2 downto 0)

);

end entity pract;

architecture behav of pract is

signal sel : std_logic_vector(0 downto 0) := "0";

begin

p1 : process(iKEY)

begin

if(rising_edge(iKEY(0))) then

sel <= sel + "1";

end if;

end process;

p2 : process(iKEY)

begin

case sel is

when "0" =>

oledg("000") <= '0'; -- this is where i get the error

when "1" =>

oLEDG("000") <= '1';

end case;

end process;

end behav;