Update: 1st May 2006. Note: if your site looks something like this
#{'head'}
#{'styles'}
#{'_BLOCK_.header.logo'} {'_BLOCK_.header.site_name'}{'secondary_links'}{'primary_links'}
#{'_BLOCK_.header.blocks'}
#{'_BLOCK_.footer.blocks'}......

there's an ERROR. Don't panic!.
(a) Just change url address to http://www.my_domain.com/user. The login box will appear.
(b) Login your username and password
(c) Select > administer > themes > [select "Chameleon" theme. Check 'Enabled' and 'Default'] > Save configuration.
(d) The chameleon theme should be displayed.
Read more about error.

If You Want Bluemarine Theme, 'Old' Bluemarine Need To Change To 'New' Bluemarine

The 'old' bluemarine theme was using the 'xtemplate' engine whereas the 'new' Drupal versions of bluemarine uses the 'phptemplate' engine. That's why error above. If we still want to use the Bluemarine theme, we need to change the 'old' to 'new'.

Go to Drupal.org and download the 2 files:
(1) phptemplate-4.6.x-1.x-dev.tar
(2) bluemarine-4.6.x-1.x-dev.tar

(3)Upload the phptemplate-4.6.x-1.x-dev.tar file in the public_html/themes/engines/[here], unzip and untar the file.
(4) Delete the 'old' folder public_html/themes/bluemarine
(5) Upload the bluemarine-4.6.x-1.x-dev.tar to folder above, extract tar file.
(6) Go to your website, login and enable admin > themes > bluemarine again. Save configuration again and we should get the bluemarine look.

That's it.