Issue Description
If you are unable to draw a simple dimension string between two points, the most common reason for this is that the Geometry Method is set incorrectly in the Info Box.
Solution
You need to change the Geometry Method to Any Direction instead of X-Y Only or Arc Length.
Please read "Arc Length Geometry Method" on this page: https://helpcenter.graphisoft.com/guides/archicad-21/archicad-21-reference-guide/documentation/annotation/dimensioning/linear-dimension-geometry-methods/