Cannot sort {0} by {1} because at least one value in {0} has multiple distinct values in {1}. For example, you can sort City ...

Cannot sort {0} by {1} because at least one value in {0} has multiple distinct values in {1}. For example, you can sort [City] by [Region] because there is only one region for each city, but you cannot sort [Region] by [City] because there are multiple cities for each region.