EEGLAB sometimes store only the coordinates of the sensors projected on a sphere or on a 2D disc, for display of 2D (disc) or 3D (sphere) topographies.
You can use these coordinates for the same purposes in Brainstorm, but not for source estimation.
Hence the warning and the recommendation to check whether you should not be importing real 3D positions instead of the disc/sphere projections from the .set file.
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