UPDATE
I ran the install again and I got further this time.
Firstly if I go to URL
http://gallery.mydomain.com/ I get the photogallery without errors and it has the look and fell of the forum which is standard.
However when I run
http://gallery.mydomain.com/adm-index.php and input my username & password which are well know to me I get the following prompt
Invalid login. Please check your username and password, or register.
This is strange as my username and password are the same as my forum and other mysql databases.
So I think its installed ok but I cant administer it,
