With the new release of Windows Internet Explorer 11 and Windows 8.1 there have been many reports from users that there Actinic software no longer uploads.
If you find that you are unable to upload or are receiving errors when attempting to upload your store then you should check to see if you computer is running Windows 8.1 or Internet Explorer 11 (IE11).
If IE has updated to version 11 then you will need to update your software to the latest version. If you are not able to update your software to the latest version then you will need to uninstall IE11.
You can read a post from one of the admins of the sellerdeck forum on how to resolve this here.