Some users may experience this error recently.

The error occurs because session values are encrypted due to subosin patch of PHP on your server (your host may upgrade php and add the patch). Who's online script enters into an infinite loop because $start_cart is undefined.

Two solutions.

1. Modify your whos_online.php file as fszone posted (#1192). Fatal error will disappear but you can't see what your customers have added to their shopping cart.

2. Remove subosin patch of your PHP or configure suhosin.ini file by adding one line "suhosin.session.encrypt=0". This can solve the problem thoroughly and you don't need to modify the whos_online.php file. Fatal error won't happen again and shopping cart works fine.

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