Dtjytyk

I've been getting exception logs for this error in production, but I'm unable to reproduce the issue in my local or staging environment, so it's been pretty hard to troubleshoot.

The error originates in Mage_Sales_Model_Service_Quote::_validate() because the $rate returned by $rate = $address->getShippingRateByCode($method) is empty.

I've added in some logging to try and get a better idea of what was going on, and I can see that $method contains the correct shipping method.

My best guess is that at some point in the process, the shipping rates are being deleted prior to when they should be.

I've noticed that every time this exception occurs, it happens immediately after a legitimate exception, such as an invalid credit card. I've tried to reproduce the issue by using an invalid credit card, then a valid one, but it doesn't reproduce for me - in staging, production, or local.

My initial hunch was that maybe the shipping method was getting lost somewhere after the first valid exception, but that's not the case, because I see that $method has the correct value at the time that this exception is thrown.

The checkout module that I'm using is AwesomeCheckout - it doesn't really to my knowledge have any custom logic when creating orders that should cause problems here, but might be related.

UPDATE: I've added in some code to attempt to recollect the rates if they are missing.

protected function _validate()
{
 if (!$this->getQuote()->isVirtual()) 

You have to understand how the rates work and how they are requested. Basically rates are requested when ->setCollectShippingRates(true) is set on shippinAddress object and it result rates to be collected and stored in rates table. This table is emptied afterwards and filled again on new rate request.

what is happening in your case is that error is thrown and request is repeated and rates are not requested but are expected to be there. So try and force the rates collection over

getQuote()->getShippingAddress()->setCollectShippingRates(true);

and then try to recollect totals as well if it does not work

getQuote()->setTotalsCollectedFlag(false)->collectTotals();

be warned that calling collectTotals multiple times can mess up your totals if some extension does not implement totals objects correctly (a common flaw)

Might have figured this out. I had a related exception that was being thrown with about the same frequency as this one, which was "The requested Payment Method is not available".

Turns out that the reason it was happening was because one of my observers off of sales_place_order_after was creating a quote object (and saving it) in order to generate some subscription pricing.

I was able to get it to reproduce by first checking out with a bad credit card as a new customer (not logged in), then going back and fixing the credit card and attempting to checkout again.

The exception was throwing because in the loadCustomerQuote observer of customer_login, it will merge your quotes together if you have more than one quote, and in so doing it loses some of the payment method information on the quote.

The fix was to delete the new quote that I was creating in my subscription observer.

UPDATE: Nope, the fix for "The requested Payment Method is not available" didn't resolve this issue, still occurring.

Just noting, sometimes PayPal Express will give an error saying "Payer not identified" upon order placement. This error stems from the same "Please specify a shipping method" exception. In Magento 1.8.1.0 this is easily reproducible by causing a "quote merge" or "cart merge" upon order placement. Merging quotes or carts will cause the shipping rates to be cleared but not recalculated. And actually, you don't want to fix this, because then the customer might be paying more than what they agreed on! Instead you'll want to remove the merging functionality - or upgrade Magento.

This is fixed in 1.9; customers first have to log in before they get redirected to PayPal .

In my case this error its originate from null value in $method and $rate

$method= $address->getShippingMethod();
$rate = $address->getShippingRateByCode($method);
 if (!$this->getQuote()->isVirtual() && (!$method || !$rate)) 
Mage::throwException(Mage::helper('sales')->__('Please specify a 
shipping method.'));

so i set a rate from this. in method and rate that available in your magento

$quote = Mage::getSingleton('checkout/session')->getQuote();
$address = $quote->getShippingAddress();
$shippingMethod = 'amtable_amtable5';
$shippingMethod = 'flatrate_flatrate';
$address->setCollectShippingRates(true)->collectShippingRates()->setShippingMethod($shippingMethod);