Really strange WSOD after submitting a form/add to cart I've read everywhere, but just can't seem to find an answer for my particular problem.

Basically when I click 'add to cart', or 'login'.  I get a white screen of death with absolutely no errors.  Error reporting is on.

For example:


I am on a product page mydomain.com/product
I click add to cart
I am not redirected to the cart page, it just redirects back to mydomain.com/product except the page is completely blank
The form still submits successfully however.  If I navigate to the cart page the item has been successfully added.
After I have viewed the cart page, by manually navigating to it in the browser.  Adding any other item to my cart works as expected.


A similar issue happens when I login to the backend.  At first I get a WSOD, but if I refresh the page it works fine.

Now here is where it gets really damn strange.  

I suspected that perhaps it was a cookie issue, so after I logged in I decided to delete the session cookies from my browser.  I was hoping that I could replicate the issue once more.  However, the problem had disappeared, no WSOD even though I had deleted my cookies.

The next day the issue returned.  I logged into the backend and the issue disappeared.  To confirm that the issue had disappeared entirely, not just for me.  I asked a friend on a computer in another building to visit the site and attempt to add an item to cart.  He said it worked fine.

Every morning the issue returns predictably and only when I login to the backend does the issue disappear for everybody for the entire day until the next day.

Has anyone experienced similar issues or have any idea what this could be?  I'm on drupal 6.26 using ubercart
I had a similar issue a year and a half ago. But in my case, it was Drupal 7 with Ubercart. Drupal had the same behaviour that you has described in your post. 

If my memory serves my right, the problem was that references to the products  when the cart is executed. They are stored in 2 different ways:


If you are a authenticated user (you have an account on a drupal site), the references to the products added to the cart are stored in database. Concretely, in a table called *uc_cart_products*. If you log out, the products remain safely in database until the user log in again. So, the user doesn't miss any information.
If you are an anonymous user (not authenticated), the references are stored in database as in step 1, but you have a radomly generated token that is stored in Cookies to identify you . The cookie has a limited time of life, so finally, the cookie will be deleted.


When the cart is built, Ubercart take that reference from cookies if it's needed and load the products. But, i had deleted some products manually from database ( i know, it's a bad deccision ), so when the system try loading a product that hadn't exist, the system failed and appeared WSOD.

To solve this problem:


I deleted manualy all lines in *uc_cart_products* database table. If you have lots of records, only delele your products. Each record has an user id or a token assigned to identify who is the user. 
Log out and delete the cookies