Error 404 "Double bar" // in google webmaster

In Google webmaster Tools , i have a lot of 404 errors with the url of the forum with double bar... (ok, but urls works perfectly)

www.website.com/forum//topic/12345-comment-in-forum

Any idea about this?

In conf_global I have:

$INFO['board_url']			=	'https://www.website.es/forum';

In forum .htaccess I changed

RewriteBase /forum/

for

RewriteBase /forum