When you check the error logs, you can see many things.
Some things you can ignore:
File does not exist: home/somtin/public_html/robots.txt
File does not exist: home/somwer/public_html/500.shtml
Some things you can fix:
File does not exist: /home/yousir/public_html/gallery/pic.jpg
The file is either in the wrong place or needs to be republished. Be sure that all of your files and folders are uploaded inside the public_html.
(13)Permission denied: file permissions deny server access: /home/sumuser/public_html/index.html
This is the most common 403 error. We can help you fix this.
error: file is writable by others: (/home/somwon/public_html/index.php)
This is the most common 500 error. We can help you fix this.
error: file has no execute permission: (/home/inono/public_html/cgi-bin/img2txt.cgi)
This can be fixed by adding executable permissions  to the file.
perhaps mis-spelled or defined by a module not included in the server configuration
This means there is something bad in the .htaccess file. Perhaps there is a php_flag line needs to be deleted.
Premature end of script headers: /home/gyms/public_html/cgi-bin/index.pl
Possibly this is a perl script and needs to say #!/usr/bin/perl -w on the first line.