Invalid Theme Warning
The 'Layout' layout of the <theme_name> theme must have placeholders named 'Title' and 'MainContent'.
Cause
You tried to set a Web Block as a layout of a theme without having the two placeholders named 'Title' and 'MainContent'.
Recommended action
Change the Web Block to have the 'Title' and 'MainContent' placeholders, or change the Theme Layout property to use a Web Block that already has these placeholders.
The <Info Balloon/Pop-up Editor/Email> layout of <theme_name> theme must have a placeholder named 'MainContent'.
Cause
You tried to set a Web Block as Info Balloon, Pop-up Editor, or Email layout of a theme without that Web Block having a placeholder named 'MainContent'.
Recommended action
Change the Web Block to have the 'MainContent' placeholder, or change the Theme to use a Web Block that already has this placeholder.
The <web block> is not a valid theme Menu.
Cause
You tried to set a Web Block as Menu layout of a theme, however, the Web Block must comply with the requirements outlined for themes.
Recommended action
Edit the Web Block and design it to comply with the requirements of a Menu Layout of a theme or choose another Web Block. Refer to the existing themes to check the necessary input parameters and entities that should be used in a Menu Web Block.