css error when clicking XML sitemap button

HI, I”m getting the following error when clicking the ‘xml sitemap’ button

Error loading stylesheet: An unknown error has occurred (805303f4)http://ozsun.com.au/main-sitemap.xsl

I’ve tried deactivating and activating the plugin, plus doing the same for the other plugins on the site but it’s still coming up.

I’m tempted to delete the plugin and reinstall it but from the support reading I’ve done it seems I’ll lose all the seo settings (and its a pretty large site). I’ve also read that if I delete plugin via ftp and then reinstall the settings won’t be lost but I can’t afford to try this if it doesn’t work.

any advice on how to fix this would be great.

thanks,
sarah

https://wordpress.org/plugins/wordpress-seo/