Site Address Change causing broken links

I have a few wp installs in subdomains of my hosting account.
I have the url I want to use forwarded to the subdom, and have the settings site address set to the forwarded domain as well.
I have one that does not work.
It seems to break page links and I think it’s my 404 settings that redirects them to my main domain.
The url in question is owned by a friend; all the rest are mine.
Would the fact I don’t own the domain make it break?
Is there something else I should be looking at?