There is not really enough information here to offer specific suggestions, however, based on your title indicting this is an application you are automating in Internet Explorer, I would try the following;
1. Try the RaiseEvent method. You may need to raise several events to get the page to recognize the click. Sometimes using the developers tools in the browser can help identify which events a particular control is listening for.
2. Here is a post that may be of some help as well.