Hi,
I don't think your $cvterm_id holds what you think it does at all.

my $cvterm_id;  # this scalar is going to be a hashref
  while (my $hashref = $sth->fetchrow_hashref) {
    $$cvterm_id{$$hashref{termname}} = $$hashref{cvterm_id};
  }
[download]

$cvterm_id is a scalar with no content at the beginning.
You get a $hashref from somewhere.
"$$hashref{cvterm_id}" is extracting the item called 'cvterm_id' from a hash called whatever is in $hashref. Eg. if $hashref = 'fred' then it's looking at element 'cvterm_id' in %fred. I'm not sure thats what you want.
Likewise the result is being written into a hash with no name (as $cvterm_id is undefined, no idea what that actually does..), in the element called $fred{termname}

If $cvterm_id is going to be a hash reference, you need to use it like this:

my $cvterm_id;  # this scalar is going to be a hashref
  while (my $hashref = $sth->fetchrow_hashref) {
    $cvterm_id->{$$hashref{termname}} = $$hashref{cvterm_id};
  }
[download]

If $hashref is also a real hash reference and not just the name of a hash, then you need this:

my $cvterm_id;  # this scalar is going to be a hashref
  while (my $hashref = $sth->fetchrow_hashref) {
    $cvterm_id->{$hashref->{termname}} = $hashref->{cvterm_id};
  }
[download]

Then the second package should work.

Try looking at the contents of $cvterm_id in the second package after the while loop, using Data::Dumper for instance. (use Data::Dumper; print Dumper($cvterm_id);)
I hope that helps,
C.
PS: Dereferencing references using the arrow operator is explained on page 253 of the Camel book (3rd edition)