why i have the error

Hi,
 i'm newbie in VHDL.
I want to creat  a output with value of a CONSTANT.
And use i the code

...................
entity dreieck_Signal is
    Port ( CLK_IN : in  STD_LOGIC; --CLK_IN = 50 MHZ
           RESET : in  STD_LOGIC;
           Dreieck_wave : out  STD_LOGIC_VECTOR(18 downto 0);
           max_count_wert : out STD_LOGIC_VECTOR(18 downto 0) := (others 
=> 0)
          );
end dreieck_Signal;

architecture Behavioral of dreieck_Signal is

signal  COUNT_UP : STD_LOGIC := '1';
signal  COUNT_DOWN : STD_LOGIC := '0';
signal   COUNTER_VAR : STD_LOGIC_VECTOR(18 downto 0):= (others => '0');
constant MAX_COUNT : STD_LOGIC_VECTOR(18 downto 0) := X"30C";
.......
max_count_wert <= MAX_COUNT;
Dreieck_wave <= COUNTER_VAR;
end Behavioral;
---------------------------
here is error:

"ERROR:HDLParsers:3384 - "Line 44. Size mismatch.  String literal 
"001100001100" is of size 12 but is expected to be of size 19."


Please help me.
Thanks you