why is my $_SESSION data not getting saved by my script when I move it to a different server?

I have a script that saves session data, and it works fine on a couple of different hosted webservers I've used it on, but I when using my local install of PHP, the session data does not persist between pages. (I set the session data on one page, and it no longer exists on the next page.) What do I need to change to get the session data to be saved properly?

I installed php using xampp for max OS X (http://www.apachefriends.org/en/xampp-macosx.html)

below is the session data from phpinfo() for my local machine (below this I'll paste the session data from phpinfo() for one of the servers where my script works -- they look almost the same):

Session Support       enabled
Registered save handlers       files user sqlite
Registered serializer handlers       php php_binary wddx

Directive      Local Value      Master Value
session.auto_start      Off      Off
session.bug_compat_42      On      On
session.bug_compat_warn      On      On
session.cache_expire      180      180
session.cache_limiter      nocache      nocache
session.cookie_domain      no value      no value
session.cookie_httponly      Off      Off
session.cookie_lifetime      0      0
session.cookie_path      /      /
session.cookie_secure      Off      Off
session.entropy_file      no value      no value
session.entropy_length      0      0
session.gc_divisor      100      100
session.gc_maxlifetime      1440      1440
session.gc_probability      1      1
session.hash_bits_per_character      4      4
session.hash_function      0      0
session.name      PHPSESSID      PHPSESSID
session.referer_check      no value      no value
session.save_handler      files      files
session.save_path      /tmp      /tmp
session.serialize_handler      php      php
session.use_cookies      On      On
session.use_only_cookies      Off      Off
session.use_trans_sid      0      0



here is the relevant phpinfo for a server on which the sessions save properly

Session Support       enabled
Registered save handlers       files user

Directive      Local Value      Master Value
session.auto_start      Off      Off
session.bug_compat_42      On      On
session.bug_compat_warn      On      On
session.cache_expire      180      180
session.cache_limiter      nocache      nocache
session.cookie_domain      no value      no value
session.cookie_lifetime      0      0
session.cookie_path      /      /
session.cookie_secure      Off      Off
session.entropy_file      no value      no value
session.entropy_length      0      0
session.gc_divisor      100      100
session.gc_maxlifetime      1440      1440
session.gc_probability      1      1
session.name      PHPSESSID      PHPSESSID
session.referer_check      no value      no value
session.save_handler      files      files
session.save_path      /tmp      /tmp
session.serialize_handler      php      php
session.use_cookies      On      On
session.use_only_cookies      Off      Off
session.use_trans_sid      Off      Off
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