Microsoft JScript runtime error: DOM Exception: HIERARCHY_REQUEST_ERR (3)

This is a bug of the Month control which is fixed in the latest sandbox build:

http://www.daypilot.org/sandbox/

The fix will be included in the next release.

Thanks for reply, but now it throw new error.

Microsoft JScript runtime error: Unable to get value of the property 'style': object is null or undefined

my code is as following

document.getElementById('DayPilot').childNodes[0].childNodes[1].childNodes[0].style.width = "400px";

You are not loading the correct node. The internal structure is not guaranteed to stay unchanged. So you should switch to a more save way to find a certain element (see .nav property of the daypilot object but remember that this is also an internal api) or update the path.