Installing WP twice on domain. Can this work?

Thanks in advance for your help.

I installed WP twice on my domain. The first /home/user/ and the second /home/user/domain/premium.

The first installation has been in existence for some time and works great.
The second installation appears fine, and the home page looks great.
Any link/post/page etc.. that is created will show up perfectly on the home page, but any click to directly view them: (examp. is a post called welcome)

Not Found (404)

The requested URL /premium/welcome was not found on this server.

Is this workable on a single domain, and if so, how?

Many thanks,

Jason