The issue is how you are indexing df. It is now required to supply both row and column indexes when you index with brackets. So instead of saying df[:RegressionTarget] you need df[!,:RegressionTarget] or you can use the shorthand syntax more simply df.RegressionTarget.
Same thing with the second error message, df[1:7] should be df[!,1:7] assuming you want columns 1:7.