dhtmlxGrid dhxCalendarA

I’m having trouble with this type of field. The example provided with the pro edition works fine but when I include it in my page, the calendar shows up at the top left corner of the page instead of next to the current cell.

When I look at Firefox error console, I have “error with analysing value of ‘left’ property” and same with top property.

I can’t find out what is different in my page compared to the example.

Any idea?