Your question, as it is written, is illogical.
In mode, the order identifier is missing . While you are checking, Magento creates a sales/quote object. This object is used to track quotation positions. It is not until the verification that the sales/order object is created from the quote.
Reason getLastOrderId returns empty because the order has not been set.
Repeating your question from the point of view of the verification process you are in and what you are trying to do with the order ID can help someone come up with some of the information that you do not know.
Good luck
Author's solution:
The problem was solved by first getting the quote id from checkout / session:
Mage::getSingleton('checkout/session')->getQuoteId();
and then specify the object by ID:
$quote = Mage::getModel("sales/quote")->load($quoteId);
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