BuddyPress.org

I don’t use XAMPP, but WAMP should be pretty much the same.

Can you confirm you ever had cookies working successfully? Even before bbPress? Sounds silly to check, but lets make sure it’s working correctly without bbPress.

Do you have the BuddyPress bbPress Integration plugin on the bbPress side? Do you have the bbPress Integration plugin on the WordPress side?

If yes and yes, the next round of trouble shooting is to make sure you have your edits exactly like the plugins say to have them.

Since you’re using MU 2.7.1, you need to have

define('WP_AUTH_COOKIE_VERSION', 1);

in your bb-config.php. This will tell bbPress how to handle your integration cookies.

That’s about all I can recommend for now?