Magento Strange Redirect Behaviour on OnePage Checkout

Question

My Magento Verison is - 1.4.1.1

I am having two problems:

1) When I am going through various steps of Onepage checkout (registration, billing, shipping, and payment tabs), sometimes during this process I am redirected to the cart page. There is no error, no exception, no report gets generated in var/report. I dont know how to debug it. Aren’t there any logs I can look for?

2) In same Onepage Checkout process after clicking on place the order (last step) , some times it redirects to the cart page, sends an email saying that the order failed with the message:

Quote totals must be collected before this operation.

To resolve it I commented this line in prepareRecurringPaymentProfiles in the file magento/app/code/core/Mage/Sales/Model/Quote.php, which solved the problem:

throw new Exception("Quote totals must be collected before this operation.");

I dont know if these 2 problems are related or not. But I am not having the 2nd problem now but having 1st one quite frequent. What could be the reason and how to resolve it?

further update-I checked the firebug trace, It is 500 internal server error which comes sometimes in any of the step in one page checkout. I was able to dig down into savebillingaction, saveshippingaction functions in onepagecontroller.php and found that error comes when $this->getRequest()->isPost() is blank , If it is 1 then it goes ahead, and goes to the next step else it redirects to cart, No I dont know why this is not 1 or is it because ajax is not able to send post data but I checked XHR request, Ajax send the post data every time (checked with firebug extension). Can Someone tell me What I could do next to troubleshoot. Where I can look for these Ajax Calls? Shipping.phtml (any step.phtml) has JS at the bottom , How does it call OnePagecontroller saveshippingaction function ?

Answer 1

Since it's internal server error, try to access the error log of the server. Will tell you where is the problem. I' ve had the same problem in 1.7.0. In my example the problem was at /app/code/core/Mage/Usa/Model/Shipping/Carrier/Fedex.php