upload package freezes at 0%

I am trying to upload an asset on teh asset store, downloaded the latest asset store tool:
-In the first phase “2.select asset folder”, the blue bar goes all the way to 100%.
-But in the second phase “3.select main assets” the blue bar freezes at 0%.

Is that a known bug and how can I fix it?

2944081--217943--temp1.jpg

After you finish the first phase, Unity opens an Explorer/Finder window on the temporary unitypackage. In some versions of Unity, the upload will hang until you close the window and return focus back to Unity.

Tried that, it didn’t fix the problem.
I noticed that the problem occurs only when I select the main assets, when I don’t, the tool completes the upload and I get the message telling me that everything gas been uploaded. So any ideas on how to fix this (I have to select the main assets)?

Why do you need to select “Main assets”? (legit question, ive never needed to use it, they make thumbnails for everything without it.)

I thought you had to select each asset so its thumbnail is previewed?