404 Not Found Not Found The requested URL /portal/ was not found on this serv

When I provide my root domain name it works fine but as root index.php file redirects to /portal/ I added [ External links are visible to forum administrators only ] in configuration file. If I do that I get above error. please help
I just downloaded new version of XML sitemap generator, and I installed it. After installing I cannot access my sitemap generator: [ External links are visible to forum administrators only ]. I received the error message:

"Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, webmaster@overproduct.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request. "

Please try to help me out. Thanks.
I am still having trouble running sitemap generator
I just re-installed the old version and ran crawling, I got the following errors:

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/overprod/public_html/generator/pages/page-view.inc.php(2) : eval()'d code on line 23

Warning: array_merge() [function.array-merge]: Argument #1 is not an array in /home/overprod/public_html/generator/pages/page-view.inc.php(2) : eval()'d code on line 23

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/overprod/public_html/generator/pages/page-view.inc.php(2) : eval()'d code on line 23

I tried to look at the code as described above, but I were not allowed to open and view the file. Please advice me what I should do next.

Thanks