In case you have problems with the custom error page for 404 or 500 errors you should create a .htaccess file in the public_html directory containing one of the lines below. If you already have a .htaccess file you should add these lines: 

• For custom 404 error page:

ErrorDocument 404 /~cpanel_username/404.shtml

• For custom 500 error page:

ErrorDocument 500 /~cpanel_username/500.shtml

The other option is to use different file names for your error pages. For example: 

• For custom 404 error page:

ErrorDocument 404 /4004.shtml

• For custom 500 error page:

ErrorDocument 500 /5000.shtml

The above directives will apply recursively to all subdirectories as well.