its due to a small error on your server you can solve this by using 2 steps
1. create a php.ini file in your public_html folder and put the code below in it just replace your cpanel username
safe_mode = off
upload_tmp_dir = "/home/YourcpanelUserName/public_html/tmp"
session.gc_probability = 0
2. replace the code of your .htaccess file with code below and here also change cpanel username
<IfModule mod_rewrite.c>
RewriteEngine On
#RewriteBase /
RewriteCond %{REQUEST_URI} ^(.*)//(.*)$
RewriteRule . %1/%2 [R=301,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^.*$ index.php?qa-rewrite=$0&%{QUERY_STRING} [L]
</IfModule>
suPHP_ConfigPath /home/YourcpanelUserName/php.ini
its working for me when i got same error last time.
