You'll probably get more attention if you post a new question, rather than attempting to resurrect such an old discussion.

The error message you get seems pretty clear to me. You are attempting to use "local" on a lexical variable - and "local" can only be used on package variables.

If you see an error message that you don't understand then it's a good idea to add "use diagnostics" to your code in order to see an expanded description of the error. In this case it says:

You used local on a variable name that was previously declared as a lexical variable using "my". This is not allowed. If you want to localize a package variable of the same name, qualify it with the package name.

But you need to ask yourself why you're doing it like this. What are you hoping to achieve by localising the variable here? I think that it's probably clearer if you create a new variable, which will be removed at the end of the block.

use strict;
my $tt = 3.14159;
{
  my $inner_tt = 3;
  print "In block, \$tt = $tt\n";
  print "In block, \$inner_tt = $inner_tt\n";
}
print "Outside block, \$tt = $tt\n";
print "Outside block, \$inner_tt = $inner_tt\n";
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Your code is further confused by the references to $::tt. Those are references to a package variable called $tt. And you never declare a package variable of that name.

You seem a bit confused about package and lexical variables. I recommend that you take the time to read Dominus' excellent article Coping with Scoping.