Gantt chart not display

I was tried to using gantt chart example.
But it gives me Uncaught TypeError: Cannot read property ‘x’ of nul.
Not getting what is this error.

My code is:
in html page :

<div data-role="content">	

<table width="100%"> 
<col width="25%"></col>
Project Name

<div id="">
     <div id="gantt_here" ></div>

In js:

 var tasks1 = {
		        {id:1, text:"Project #1",start_date:"01-04-2013", duration:11,
		        progress: 0.6, open: true},
		        {id:2, text:"Task #1",   start_date:"03-04-2013", duration:5, 
		        progress: 1,   open: true, parent:1},
		        {id:3, text:"Task #2",   start_date:"02-04-2013", duration:7, 
		        progress: 0.5, open: true, parent:1},
		        {id:4, text:"Task #2.1", start_date:"03-04-2013", duration:2, 
		        progress: 1,   open: true, parent:3},
		        {id:5, text:"Task #2.2", start_date:"04-04-2013", duration:3, 
		        progress: 0.8, open: true, parent:3},
		        {id:6, text:"Task #2.3", start_date:"05-04-2013", duration:4, 
		        progress: 0.2, open: true, parent:3}
		        {id:1, source:1, target:2, type:"1"},
		        {id:2, source:1, target:3, type:"1"},
		        {id:3, source:3, target:4, type:"1"},
		        {id:4, source:4, target:5, type:"0"},
		        {id:5, source:5, target:6, type:"0"}

gantt.parse (tasks1);

try setting a fixed size to the gantt container

<div id="gantt_here" style="width:800px; height:600px;"></div>

thanks for reply…
But one thing I observed…
I am using ganttchart and chart in my application . I included
for chart

for ganttchart

then application gives me “Uncaught TypeError: Cannot read property ‘x’ of null” this error when these two js are included.

But when i remove this script from index.html
the application working fine. Means not gives any error and ganttchart create on page without any error.

Please suggest me any solution for this.
I want to use charts and ganttchart both in my application.