Based on the new description it is not obvious to me what the problem is exactly.
- What Slicer version do you use?
- How did you segment the lesion? Using Segment Editor?
- How did you save it?
- How are you trying to load it?
For reference, my answer in the thread this question originally appeared:
Import: drag&drop nrrd on Slicer, and in the popup window, choose Segmentation in the Description column.
Export: if you want to export the segmentation as a single nrrd file (all segments in the same file, which means overlapping segments are not permitted), then you can export the segmentation into a labelmap in the Segmentations module or in the Data module by right-clicking the segmentation, then click the Save button and save the labelmap as an nrrd.
As a side note, next time please create a new topic instead of commenting a new question to an only tangentially related topic. Thanks!