I have a sketch, just a rectangle: 0,01mm by 0,001mm
NX refuses to extrude this. It responds with an alert: Missing section string.
When I change the value from 0,01 to 0,03 it will extrude.
Which Setting in NX is responsible for this behaviour?
If the length is smaller than the modeling tolerances, NX might be ignoring the object. Try changing your modeling tolerance to something much smaller than the smallest distance that you will be working with. Preferences -> modeling -> distance tolerance will change the modeling tolerance for the current part. If you want to make this your default when creating new files, you may need to update the setting in your template parts and/or your customer default file.