Have you checked the value of $in{tax_id}?

e.g.

if ($in{tax_id} ne "") {
   warn "updating $username tax to $in{tax_id}";
   $dbh->do (qq{ UPDATE reg_users SET tax_id = ? WHERE username = ? },
                    undef, $in{tax_id}, $username) || error("Error on 
+MySQL Update: $DBI::errstr");
 } else {
    warn "Not updating tax_id for $username (\$in{new_aff} == $in{new_
+aff})";
 }
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If you don't see a warning then the code isn't be executed for some reason. If you do see a warning, then you'll know exactly what's going on.

rdfield