Before you can proceed, you'll need to set your email size and padding in Content Settings (without px). Learn more.
This error will display in the email editor if you're editing an email that uses a standard HubSpot layout and email size and padding settings haven't been defined in your email settings.
To resolve, please navigate to Content Settings > Email. Choose Marketing > Email from the left side, then select the Configuration tab. In the Size section, enter numeric values for those properties (without entering the letters 'px').