Sitemap : Error 500

I have recently installed this plugin. Everything is working fine except the sitemap generator. When ever i click on “XML Sitemap” the page redirect to :

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator and inform them of the time the error occurred, and the actions you performed just before this error.

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

I have even tried to use the fix in htaccess but even that couldn’t get the things working for me..

Kindly guide me on how to fix this error.

https://www.ads-software.com/plugins/wordpress-seo/