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If they are the same CRS then the GIS source has made some error in the new file or corrected some error in the old.
If they have a different Geographic Coordinate System then look at Transformations in the Data Frame Properties and make sure the correct one is set for transforming the GCS of the new layer to that of the Data Frame and presumably of the original layer.
The other question is: how do the shapefile line up against some reference like one of the "Add Data from Resource Center" maps in the main ArcMap menu under "File"? This is usually a good test especially in high precision areas of the eastern seabord and southe Canada and more convenient than importing the shapefiles into Google Earth or indirectly comparing a few spot coordinates.
If you can post the CRSs of the two files and a screenshot of their alignment relative to the Resource Center maps that would help clarify the problem.