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The grid could not be rendered with function grid.printPreview() / smart rendering case as you scroll slide bar from Top to Bottom.
Reason: I guess this function did not ignore (skip) empty row(s) during the rendering process.
Error msg: 'this.rowCol[...].idd' is null or not an object

Not much can be said in addition to the reply above, but you also can check functions of anther and colspan all and find out what we have probably missed in our explanation.