ELEVATION IS NOT PERPENDICULAR TO VIEW

PROBLEM:

An elevation is no longer perpendicular to what it is elevating. (See SECTION IS NOT PERPENDICULAR TO VIEW for sections with this problem)

You may notice this when you try and add dimensions to your elevation view and Revit won't pick them, or Revit crashes.

POSSIBLE CAUSE:

Revit requires elevations to be EXACTLY perpendicular. If they are out by 0.0000000012mm you may get errors and crashes.

When placing the elevation Revit snapped to the wrong element.

What is being elevated has been rotated (e.g. a wall's angle has been changed due to a design change).

SOLUTION:

Select the elevation reference, pick the little rotate symbol bottom left corner of reference, move your mouse until the reference snaps to what you are elevating.

DO NOT use the Rotate command - it will not snap to any element and so not be correct.