It looks as if you are running windows. Unfortunately, there have been several reports like yours from windows users who run LTK. But I have never been able to reproduce this behaviour (I do not have a windows box but whenever I ran LTK on a windows machine it worked for me).
From what other users reported, your problem can come from a program
running in the background, like a tray program. Try to disable all of those to find out which one may be the culprit. If you find it, please tell the list, so we can create an issue list.
Peter