I've struggled with logins as well. You might want to try using HTTP::Cookies. I had a problem that went away when I did things with HTTP::Cookies, though I don't really understand why. FWIW:

use strict;
use warnings;
use HTTP::Request::Common; # HTTP handling
use HTTP::Headers;
use HTTP::Cookies; 
$cookie_jar->clear; 
my $cookie_jar = adwordsLogin($adwordsLogin{login},$adwordsLogin{passw
+ord},$adwordsLoginWait,$options{language},$proxy);
my $ua = LWP::UserAgent->new;
$ua->cookie_jar( $cookie_jar );
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