@sortedCollectionData = sort {
    $collectionData[ $b ]{CollectionId} <=> $collectionData[ $a ]{Coll
+ectionId}
    ||
    $collectionData[ $b ]{Modified} cmp $collectionData[ $a ]{Modified
+}
    } 0 .. $#collectionData;
[download]

What you are storing here are numbers (specifically from 0 to $#collectionData), so @sortedCollectionData now contains these numbers in some order or another. And then you write $sortedCollectionData[$i]{'Status'}, and try to access one of these numbers as if it was a hash reference.

You might want to sort your hash refs directly instead:

    @sortedCollectionData = sort {
    $b->{CollectionId} <=>  $a->{CollectionId}
    ||
    $b->{Modified} cmp $a->{Modified}
    } @collectionData;
[download]