Hi Anna,
Hope you're doing well!
The google error is unclear, I can load your sitemap fine so if you are indeed talking about the 4SEO sitemap, then I suspect Google may have tried to read it before it was ready? This should definitely clear up as the sitemap is there and working.
As for the stylesheet error, it is your server blocking access to it:
It might be your .htaccess, or a setting in your control panel. As usual, if you're running Admin Tools, that's the first place to look as it tends to block a lot of things by default. Make sure that **.xsl file can be access normally and not blocked.
Note that not being able to access the stylesheet should not cause any problem to Google, the stylesheet is only for visual display of sitemap but Google should not care about that, they are only interested in the content of the sitemap.
Best regards
Yannick Gaultier
weeblr.com / @weeblr