Hi Jesus,
Thanks for supplying the error. Unfortunately, I wasn't able to replicate the issue you're experiencing. By default, the permalinks plugin should ignore any physical file or directory that exists. You can try to explicitly ignore that directory by updating the permalinks code in your .htaccess to something like this (the paths may be different for your installation):
### Pass URL to permalinks dispatcher (do this last after any other redirects)
RewriteRule ^permalinks_dispatcher\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !myadmin
RewriteRule . /cmsb/plugins/permalinks/permalinks_dispatcher.php [L]
If that doesn't solve the issue, it might be easier for me to take a look directly. You can fill out the Support Request form (https://www.interactivetools.com/support/request/ - select 2nd level support) with the connection details of your site, and I'll see what I can find out.
Cheers,
Daniel
Technical Lead
interactivetools.com