Is this occurring for all components? If yes, the path for LBT scripts has not been set. Check if you have ran the BAT file in the process of installing LBT. If the error repeats even after running the BAT file, please go through the link below shared by @chris to add LBT to Rhino Python Path.
How to Manually Add Ladybug Tools to the Rhino Python Path - ladybug-tools - Ladybug Tools | Forum