GET variables causing problems

I’m using aweber to get subscriptions, and when it returns to a thank you page on my blog, it throws an error.

https://www.abc.com/resources/newsletter/thanks?custom%20address%201= (snipped) throws a 404 page, but

https://www.abc.com/resources/newsletter/thanks works.

Is there any way to get WordPress to ignore the GET variables? Or is my .htaccess file the problem?

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

# END WordPress

Thanks!