ERR_TOO_MANY_REDIRECTS with .htaccess using two different CMS's

I have two setups installed on my hosting, the first one is a php script to track shows and etc, is in the root folder, it contains a .htaccess file, the second one is a forum, installed in /forum/, it won't let me do anything with the forum folder unless I remove the first CMS from the root folder, so afther that It will allow me to acess to it, the thing is I don't know what is causing the redirects.

This is the .htaccess file located in the root folder.

<IfModule mod_rewrite.c>
    RewriteEngine On

    ##
    ## You may need to uncomment (remove #) the following line for some hosting environments,
    ##
    # RewriteBase /

    ##
    ## Uncomment following lines to force HTTPS.
    ##
    # RewriteCond %{HTTPS} off
    # RewriteRule (.*) https://%{SERVER_NAME}/$1 [R,L]

    RewriteCond %{REQUEST_URI}::$1 ^(/.+)/(.*)::\2$
    RewriteRule ^(.*) - [E=BASE:%1]

    RewriteCond %{REQUEST_URI} !^public
    RewriteRule ^(.*)$ public/$1 [L]
</IfModule>