Users to my store (http://reliablegokarts.net/store/index.php) are being logged off while shopping and/or checking out. It seems to be random, and requires signing in again to get the shopping cart back.

My host is Powweb, which recently changed platforms. I'm running 1.2.4, PHP 4.4.4, on an Apache server running MySQL 4.1.18. The store has been up for about a year; this problem just started.

I am a novice at e-commerce, and your assistance is greatly appreciated.