can you use Data::Dumper to see which is the offending file? I guess it means that there's a file where the mtime or ctime is empty... (Update {after reading McDarren's reply} Probably see that one of the elements in @files is undef OR one of the elements in @files is a file that does not exist/can't be stat'd)

use Data::Dumper;
print Dumper [  map { [ $_, [stat]->[10], [stat]->[9] ] } @files  ];
[download]

Also note that while it said "line 54", lines 54,55,56 (which has the <=>),57 are all the same statement.