The smallest dimension of the columns cannot be smaller than 300 mm.
The Complete Message:
Smallest cross-sectional dimensions of rectangular columns cannot be smaller than 300 mm. (TBDY 2018 7.3.1.1)
In the article 7.3.1.1 of TBDY 2018, it is stated that the smallest cross-sectional dimension of rectangular columns shall not be less than 300 mm. You are warned because this condition is not met.
Solution
Give the size of the arm with the name and solid at least 300 mm.
Select column, columns
Click the Column Dimensions icon on the right toolbar.
In the opened Column Dimensions dialog, write at least 300 mm in the column long edge direction and column short edge direction.
Click the OK button.