1.9.2 installation failure

It is the first time for me to install Piwik.

I have uploaded the piwik installation file via FTP in binary code, and tried to start the installation in the browser, but it failed with the following information:

Error: Unable to start session. Please check that the web server has enough permission to write to these files/directories:
For example, on a Linux server if your Apache httpd user is www-data, you can try to execute:
chown -R www-data:www-data /www/users/xxx.com/a/piwik/tmp/sessions/
chmod -R 0755 /www/users/xxx.com/a/piwik/tmp/sessions/
Debug: the original error was
session has already been started by session.auto-start or session_start()

I have asked the host service provider to help me execute the commands above but the problem still exists.

Any suggestion will be greatly appreciated.

I would search for " session has already been started by session.auto-start or session_start() " and try find a solution as this is not a piwik issue