Hi,
Thanks for your reply.
OK, I finally got it working!
I have been installing the site on another unused Domain on my Web Server as a testing zone before I go live. I think I have probably tried moving my MAMP version to the Server over 20 times with different combinations of uploads before I finally got it working.
Anyway, if anyone else is having any problems moving their site over, this is what worked for me –
(Web server running Ubuntu Linux, MySQL version 5, PHP5).
1. Logged in to Web Server and created a new MySQL database.
2. Installed a full, clean installation of ModX (1.0.4).
3. Amended the ht.access file to include the paths to the Domain :
# Rewrite domain.com -> www.domain.co.uk -- used with SEO Strict URLs plugin
#RewriteCond %{HTTP_HOST} .
#RewriteCond %{HTTP_HOST} !^www\.domain\.co.uk [NC]
#RewriteRule (.*)
http://www.domain.co.uk/$1 [R=301,L]
4. On the Web Server, changed the name of ht.access to .htaccess
5. Logged in to ModX, and saved the Configuration that appears when you first log in.
6. Logged out of ModX.
7. Logged in to my Web Server Admin, deleted the Database created in step 1.
8. Created a new Database with the same Username and Password as the one just deleted. This is important as the ’config.php’ was updated with these details during the installation of ModX.
9. Export the Database from the working copy of the site on your computer (in ModX : Tools -> Backup), and save this file onto your computer.
10. Back to the Web Server; import this database backup file into the new MySQL database.
11. Uploaded the ’Assets’ folder from my working MAMP site onto the Web Server, overwriting the ’Assets’ folder from the clean installation of ModX.
12. Logged back into ModX, saved the ’Configuration’ page that appears.
13. ’Tools/Configuration/File Manager’ : check that the ’File Manager path’ is set correctly (should be something similar to - /home/d/domainname/public_html/)
And that did it!

I didn’t need to change any Permissions on the Assets folders at all. This is very slightly different than the example in the ModX Wiki; each Hosting company/Web Server may have slightly different ways of dealing with files etc.
At the end of all this I think it was copying the ’/manager’ folder from my working MAMP files onto the Web Server that seemed to cause me problems.
Hope that helps anyone with similar issues.
Cheers.