Mika, thank you for the reply.
1) The sites worked for about a day after I installed WP multi-site, then started getting the error message when trying to visit them.
2) Is this what I was supposed to do? Still getting the error message on site URLs and published posts/pages, but now I can see post/page previews.
RewriteEngine On
#Replace ?mysite\.com/ with your blog url
RewriteCond %{HTTP_REFERER} !^https://(.+\.)?hostingbarato\.biz/ [NC]
RewriteCond %{HTTP_REFERER} !^https://(.+\.)?switch-marketing\.com/ [NC]
RewriteCond %{HTTP_REFERER} !^https://(.+\.)?trampolinereviewsonline\.com/ [NC]
RewriteCond %{HTTP_REFERER} !^$
#Replace /images/nohotlink.jpg with your "don't hotlink" image url
RewriteRule .*\.(jpe?g|gif|bmp|png)$ /images/nohotlink.jpg [L]
3) Could the domain mapping plugin settings be causing this? I have options 1, 3 and 4 selected.
Thanks for your help