I would highly suggest you do not take an approach like this. Exception based errors (die/eval) are far superior in many respects. If you are not convinced yet, do some research (PBP, Modern Perl). Also look at all the monks! Most have already suggested die() and for good reasons!

Also, in errorstr() I think I see a bug:

$self or return $ERRORSTR; # Class call
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I think you meant to do this?

ref $self or return $ERRORSTR; # Class call
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But more importantly, use exceptions instead!