Hi Roni, so the reason why your object isn't a solid is that edges need to be no more than 0.005 units apart from one another in order to be joinable and your surfaces have many areas with larger gaps than that.

Each of your surfaces has at least one edge that is close enough to another to get joined, but not all edges. So that's why it selects as one connected object because it is connected together through some edges but not connected in other areas.

To get it into a solid all edges need to be connected, not just some of them. So some pieces need to be deleted and remodeled with higher accuracy to get it into a solid.

To find out where you have open edges you can set up a script on a shortcut key as described here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2

Then you need to inspect those areas closely to see what is wrong there, you can use the Zoom Area viewport tool to do that, here are some areas that I saw with a couple of initial looks:


There are some big gaps along the bottom strip:



- Michael