HELP: Non-manifold edges found for part ...

Hi all,
I'm an chinese student trying to use HFSS .
I created a model and I was trying to validate it but there should be some problems about it; does anybody know what this message "non manifold edges found for kongqiang1" means?
Please help me! Thank you very much!

---------- Post added at 15:45 ---------- Previous post was at 15:40 ----------

here is my model,please help me and tell me the fault~

Non-manifold means that some geometries have mixed dimensions and cannot be manufactured. In your case you have a 3D object which touches itself at a point or edge, look at the picture bellow:

Your circular tubes are to close to the the middle tube.Try to expand the the thin edge pointed with the red arrow in the picture. Use the "Clip pane" tool to show inside the object.

Thank you for your help! Thank you very much!