The solution is not to update "System - Helix Ultimate Framework" site plugin. For me it stops working when I update from version 1.1.4 to 2.0.2. You can update Joomla core including all extensions to the latest version except this plugin.
If you are updating the Helix Framework, then you need to disable the Advance Template Manager. You can choose what is more important to you, or wait for a new version of the Helix template where they fix it. For me is more important Advance Template Manager.
hello bro, can you help me? I have the same problem which is "Default Layout File Is Not Exists! Please Go to To Template Manager And Create A New Layout First.", but I haven't found the solution.