I had this problem for over a week, and tried so many things that I don't know what eventually fixed it but the best call is:

• create a new project
• access the asset store
• import the asset store tools
• log out from the asset store

• start the asset store tools <= if you receive an error telling that you need to log in, from here on it's easy, otherwise you'll have to fill a bug report, otherwise =>

• save project and quit unity

• reopen project and access the asset store, I found out I still was logged in, so log off
• restart the asset store tools, log in and it should work