To chat with others, they also need to have their chat enabled. Unfortunately too many people are not educated into enabling this.

You can check if others have their chat enabled by right-clicking the heading bar of any window be it the search results or download window or upload window, & choose show Chat from the drop down menu. The heading bar is the one at the top of any window that shows file name, file size etc. That particular horizontal column has extra show vertical columns if you right-click upon it.

Sorry for late responses, I've been drifting in & out of the forums with private things to do.