NOTE: When making a new post, be sure to include relevant information such as:
What version of Zen Cart are you using? v151
Has your site been upgraded? When? From what version(s)? no
What version of PHP and MySQL is your server using? (See Admin->Tools->Server Info) PHP 5.3.27 MySQL 5.1.56
WHEN did the problem "start"? How does that compare with other events of your hosting company, changes you've made to your site files/addons, or your admin settings, etc? My host upgraded from PHP 5.2 to 5.3.27 and immediately, a few customers began complaining that their cart would timeout when they hit the final button to complete their order. The PHP upgrade was the only thing that has changed on my installation for several months.
Please post your site URL* so we can take a look at it. This is especially important if you're encountering display/layout problems, so the problem can be seen directly. laurelsstitchery.com
If you're encountering problems that could be related to your server or hosting company, include the name of your hosting company (not their URL). Dreamhost
HAVE YOU LOOKED IN THE FAQ AREA for answers to your question? (ie: a search for your error message or what you want to edit/change, etc) yes
Have you searched the FORUM for your error message or for answers to the question you're asking? yes, but the other threads are older and no one mentioned having upgraded PHP recently

As mentioned above, my host upgraded PHP from 5.2 to 5.3.27. Of course, this happened during my Thanksgiving sale, so the site was getting a lot of traffic. Within the hour, I received an email from a long-time customer complaining that the cart had timed out when she hit the final button to complete her order. After a couple of attempts, she was able to log back in and complete her order. I wrote it off to her walking away for a while and the normal time-out occurring.

On 11/30, I was entering my usual batch of manual orders. After a few completed correctly, I got the same session time-out error. A couple of times, I was able to log right back in and complete the order and a couple of times, I had to dump all cookies before I was able to log back in. Highly annoying.

The error is still occurring today. I'm convinced this is the fault of the PHP upgrade. I don't know where to start on getting it fixed. Any help would be appreciated.