You have clicked some points for your dimension string. You have not checked the geometry method for the correct orientation, horizontal or vertical. Well over half the time, due to Murphy's Law, the wrong one is selected. You click to place the string, and get nothing. You have to start over. You are sad.
If you are dimensioning walls, you should be clicking on the line of the wall, rather than the corner, in order to dimension the core. (This isn't the tip; it is current standard practice. I hope someone is praying for you if you aren't dimensioning this way.) Choose the third, arbitrary angle, geometry method. With this setting, the string is forced to orient perpendicular to the wall, regardless of the wall's direction.