Two or more slab areas or beams with the same priority overlap at (x,y)

Overlapping slabs and beams should have different priorities. This is explained in "The priority method".

The error is generated when two or more overlapping slab or beam objects have the same priority.

To fix this error

Choose Layers > Mesh Input Layer > Standard Plan.
Choose View > Visible Objects ().
Note: You can also right click to see a popup menu that includes the Visible Objects command.
Check the Priorities boxes under Beams and Slab Areas, then click OK.
Use the coordinates in the error dialog box to find the location of the problem, and revise the assigned priorities. Usually this requires making sure that the thickest slab or beam have the higher priority (the lowest priority is 1).

Note: The highest priority is not always assigned to the thickest element. For example, where a standard slab area overlaps a depressed slab area.