So it appears that your forum root is below your user account root, such as /public_html/forum and your .htaccess is being written to /public_html. It also appears that you cannot change the RewriteBase and you cannot change the location of the .htaccess file. I'm guessing here that you are using a free host due to so many restrictions. This combination WILL NOT WORK.
In order to make VBSEO work you must a) alter the RewriteBase, which you apparently cannot do, b) change the location of the .htaccess file, which you apparently cannot do, c) move your entire forum root to your account root, which you can do, but I'm not sure if you would want to, d) change hosts to something less restrictive, or e) forget about running VBSEO - it's not really necessary.
These are your choices. By the way, I am no one's boss - I'm married.