Your OPEN statement :

open(GRADES,"<<$grades") ...
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is incorrect - it is taking the second "<" as a part of the file name.

Follow graff's advice above., or (better), consider using local file handles in addition to the 3-arg open, and avoiding single-use throwaway variables:

open (my $grades, "<", $self->{gradefile})
  or die ....
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I might have gone further to suggest what I usually do - save the file handle as a part of the object, like:

  open ( $self->{gradefh}, "<", $self->{gradefile})
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but this makes it tricky to read/write the file - you need extra braces.