Export project gives empty assets

I have a problem when I try to export a projet to an another computer (both with Unity version 5.0.1f).

I use this path Export Package → All → Select Dependencies and when I import the project I select custom package. Everything is imported without any problem, except the assets which are visually empty in Unity even if the file has the same Ko as the model. So when I drag and drop them in the project to test them, nothing is visible, nor in the inspector or in the preview.

How can I import a project keeping the assets visible?

If the intent is to transfer the entire project to another computer you do not need to export the project. Either zip it up and transfer the zip file, or use a cloud syncing service such as Dropbox or Google Drive to keep the project synced between the machines.

Of course the best way of doing this is setup source control, either with GitHub or Bitbucket as both of them have easy to use interfaces.