Thread Subject: Error message "Scalar structure required for this assignment"

When I run this fragment

.....................................

 if Scan(1).Reach <= 300
     o = 1;
    % Left end marked.
      Map.Object(o).LeftMarker = 0;

    end
.....................................

I get this error message

....................


??? Scalar structure required for this assignment.

Error in ==> C:\MATLAB6p5\work\Develop03.m
On line 31 ==> Map.Object(o).LeftMarker = 0;

..........................................

And I can't see why. I've assigned numerical values to fields of
structs often enough and no problem. Why this time?


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