The panel has to be supported at the start and end of it; this means that a support is required here. If this is not the case, the message shown in Image 01 appears.
If there is a free edge, add the support manually. The support can be specified in Column C and Column D in Table "1.7 Cross-Section Parts for Classification According to EN 1993‑1" or in the "Edit c/t-Part" dialog box (Image 02).
The panel shown in Image 03 includes Elements 1 through 3. However, the elements have no support at their free ends (marked red in Image 04), so the error message shown in Image 01 appears. The support must be added (Image 05) to enable the calculation. This is also shown in the video.