If you are wanting to use different more than one session on the same domain, (i.e. if you have several versions of the same login system in different folders or subdomains), you need to name your session before calling session_start();

For example:

// Start Session & starting vars
session_name('name1');
session_start();

There are only a few limitations to the characters… You can only use characters: a-z, A-Z and 0-9, no . so camelcase is probably wise…