Global Site Tags Breaks Simple:Press Forum (404 errors for all links)

I installed Global Site Tags plugin, and all my forum links (Simple:stuck_out_tongue:ress Forum v4.1.2) give "404 page not found" errors. When I disable this plugin, everything works OK.

When I disable permalinks, everything works fine... but, of course, this is not a solution, as it effectively kills all links to my site. Enable permalinks again brings back the err

I'd be grateful if you could point me in the right direction to look to fix this. Below is the content of my .htaccess file

RewriteEngine On
RewriteBase /

#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-content/blogs.php?file=$2 [L]

# WPMUDev Sitemaps and SEO
RewriteRule ^(.*/)?sitemap.xml wp-content/sitemap.php [L]

# add a trailing slash to /wp-admin
RewriteCond %{REQUEST_URI} ^.*/wp-admin$
RewriteRule ^(.+)$ $1/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-.*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

<IfModule mod_security.c>
<Files async-upload.php>
SecFilterEngine Off
SecFilterScanPOST Off

Thank you.

EDIT: I can see user "jcnjr" has a similar issue with Site Search and Directory plugins, but that post is not resolved either.