I'm running Zen Cart v1.3.9h, and PHP Version 5.4.45. My website was installed in 2010, and has been "Heavily Modified" over the years. I do not sell physical products, but instead my products are "Training Class Dates", and my customers purchase a "Seat" in my classes!

I know that I should have updated my site (probably long ago), but it would be a nightmare with all of the modifications. The site works well, however only once in awhile a customer will call to tell me that when they went to login to their account, they found that they were "Already Logged Into Another Customers Account"!!!

I have seen this myself a few times by simply visiting my main page, and refreshing the page! I would then already be logged into a customers account that had just purchased a seat in a class from my site! If I Logout, then all is back to normal, and I can login myself just fine!

Like I said, it does Not always happen, and I can't recreate the issue, but I've seen it about 4-5 times in a year, but hard to know how much it happens to other customers!

Does anyone have any ideas?
Thanks in advance.....!