Not all versions of your page point to the same URL

HI There

im using version 4.2 and trying to improve SEO.  if i run a an seo audit on the site i get an issue with https://www - URL  not resolving correctly

Warning, no 301 redirects are in place to redirect traffic to your preferred domain. Pages that load successfully both with and without www. are treated as duplicate content!

Not all versions of your page point to the same URL.

URL   Resolved URL
http://WEBSITE.CO.UK/ =. https://WEBSITE.CO.UK/

http://www.WEBSITE.CO.UK/=  https://www.WEBSITE.CO.UK/

https://WEBSITE.CO.UK/  = https://WEBSITE.CO.UK/

https://www.WEBSITE.CO.UK/  error - 500

Is there somewhere that i can change this ?

THANKS !

The setting "Force SSL for all site pages" is used to force SSL for the entire site
Is it set to true ?
See Administration -> Configuration -> Settings -> General Settings

Yidna wrote:

Thanks for the reply. It was unticked. Ive ticked it now - BUT  thats caused the "non https" verions to now give a 500 error !

i also have a warning : Specified store URL (https://www.website.co.uk/) doesn't match this store URL (http://website.co.uk/)

eeek any ideas?? is there somewhgere i need to enter something else?