I posted this topic below
http://mindfusion.eu/Forum/YaBB.pl?board=fcnet_disc;action=display;num=131709203...

You told me should download new version, I did. I set properties of Diagram like below:
AlignToGrid = false; // I think this is the place problem is
MeasureUnit = Display; // Maybe it is too
LinkHitDistance = 4; // Maybe it is too

Case 1:
I move mouse on a link exactly and click, I find I can not select the link. I move mouse beside a link(distance maybe is 2 pixels, of course it is less than 4 pixels) and click, I find I can select a link.

Case 2:
Set property AlignToGrid of Diagram to true. It can work perfectly.

But there is a difference. In Case 1 link is thinner than in Case 2. Tow links in tow cases are vertical absolutely.

Could you help me to solve this problem ?
Thank you a lot.