I can access my gallery but not an album.. Help please?

Hi. I'm getting the following error when I try to access the album in my gallery:
"Forbidden
You don't have permission to access /rainbow/Rainbow-Bridge/ on this server."
I've just updated to v1.5. Got through the Config Wizard. Then started getting the above error message.
From searching the forum it seems like this is a file CHMOD problem, so here is what some of the files are CHMODed to.
Setup folder: 400
.htaccess: 644
config.php: 644
most other php files are 644

I can access the gallery if I go to http://www.pets-express.co.uk/rainbow/index.php but I can't access the album at http://www.pets-express.co.uk/rainbow/Rainbow-Bridge
Before I upgraded to v1.5 the gallery was accessed by going straight to the album i.e. I didn't (and still don't) want an index page.
Anyone have any idea where the answer to this is?

Added: I noticed that some gallery files had different "ownership" to the rest. My FTP program said they were owned by "99" and I couldn't CHMOD them. So I got my hosting company to change the ownership to match the majority of the gallery files. My FTP program confirmed that they had changed the ownership back. I cleared my cache, rebooted and then tried to access the album, but got the same errors as above. I went into my FTP program and the ownership of the files had reverted to "99".
The tech guy at my hosting company says that the script is changing the ownership of the files.
I hope someone can help me with this as it's very frustrating.

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The following information is required to get an answer:
Get this information from the PHP diagnostic (in the configuration wizard).
Gallery URL (optional but very useful): http://www.pets-express.co.uk/rainbow/Rainbow-Bridge
Gallery version: 1.5
Apache version: 1.3.33
PHP version (don't just say PHP 4, please): 4.3.11
Graphics Toolkit: ImageMagik
Operating system: Windows XP
Web browser/version (if applicable): IE6