Selecting multiple checkboxes by using DataGridCheckBoxColum

   I m trying to create a DataGrid which will have DataGridCheckBoxColumn  . I have bound DataGridCheckBoxColumn to certian values coming from database. I m even able to select the checkbox but as soon as i selected a checkbox the previous one gets deselected. Means it is acting like a radio button.

Also when i m trying to select a checkbox i have to click it twice or else it does not get selected.

Kindly help me to solve the problem asap.