Community @ The Turning Gate

I have watched and read the tutorial on how to install - but am not able to get it working.
When I install the files as per the tutorial to my root directory, I get as far as installing it and logging in with the admin username and password, and to the screen where you input your site settings. When I try to save settings I get this error:

session_start(): open(../backlight/data/sessions/sess_9c3b0dde6936fbcab51db85df0773eb3, O_RDWR) failed: Permission denied (13)|#0 [internal function]: ErrorHandler::handleError(2, 'session_start()...', '/home/lisalpho/...', 156, Array) #1 /home/lisalpho/public_html/backlight/modules/module-framework/helpers/AuthHelper.php(156): session_start() #2 /home/lisalpho/public_html/backlight/modules/module-framework/Framework.php(390): AuthHelper::handleSession() #3 /home/lisalpho/public_html/backlight/modules/module-framework/Framework.php(148): Framework->handleSession() #4 /home/lisalpho/public_html/backlight/modules/module-framework/Framework.php(41): Framework->init() #5 /home/lisalpho/public_html/backlight/index.php(31): Framework->__construct('..', Array) #6 {main}|URL: /backlight/index.phpfile_put_contents(../backlight/data/class_lookup.txt): failed to open stream: No such file or directory|/home/lisalpho/public_html/backlight/modules/module-framework/helpers/ClassFinder.php|113

My other problem is that I am running Wordpress for my website, so when I put the Backlight2 files in my root directory it replaces my wordpress index.php file and therefore no one can access my site - it goes directly to the Backlight2 installer.
I tried creating a new folder in my root directory (called ttg), put the unzipped Backlight2 files in this and got as far as the same point above, and got what seems to be the same type of error message:

session_start(): open(../backlight/data/sessions/sess_9c3b0dde6936fbcab51db85df0773eb3, O_RDWR) failed: Permission denied (13)|#0 [internal function]: ErrorHandler::handleError(2, 'session_start()...', '/home/lisalpho/...', 156, Array) #1 /home/lisalpho/public_html/ttg/backlight/modules/module-framework/helpers/AuthHelper.php(156): session_start() #2 /home/lisalpho/public_html/ttg/backlight/modules/module-framework/Framework.php(390): AuthHelper::handleSession() #3 /home/lisalpho/public_html/ttg/backlight/modules/module-framework/Framework.php(148): Framework->handleSession() #4 /home/lisalpho/public_html/ttg/backlight/modules/module-framework/Framework.php(41): Framework->init() #5 /home/lisalpho/public_html/ttg/backlight/index.php(31): Framework->__construct('..', Array) #6 {main}|URL: /ttg/backlight/index.phpfile_put_contents(../backlight/data/class_lookup.txt): failed to open stream: No such file or directory|/home/lisalpho/public_html/ttg/backlight/modules/module-framework/helpers/ClassFinder.php|113

Can someone help? I am lost