I suspect it's a browser issue, not a platform issue .. What browsers are they using on the PC's? on the MAC? Most importantly, are cookies enable on the PC browsers?? is your site blacklisted in their browser? Might be useful to google for "cookie check" and have them try one of those sites, to see if it's all cookie sites or just yours ..

Some code comments:

In reply to Re: Why cookies do not work on some users' windows PC? by davidrw
in thread Why cookies do not work on some users' windows PC? by clickit

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