Blog post URL resolving to main domain, not subdomain...

Hi,

Here's the blog successfully installed: https://holmesbrand.com/camberleighhay/blog/

But clicking on the post resolves to the primary domain, rather than the subdomain:

https://holmesbrand.com/blog/post.php?s=2014-06-20-cheltenham-jazz-festival

And I get an error saying 'no input file specified'

If I put the subdomain name into the post URL manually, I can see the post:

https://holmesbrand.com/camberleighhay/blog/post.php?s=2014-06-20-cheltenham-jazz-festival

As far as I can determine, everything is correct in the directory structure. Can anyone suggest what might be causing this issue? I haven't been able to find anything similar in the forum or online.

Many thanks, James