I've noticed recently on DL.com that if you search for award travel, but don't have enough miles in the account (for example, you plan on transferring miles from AMEX to DL), you can't complete the search. You get 99% of the way there (you can choose both the outbound and return segments), but when you try to go to the next page to see clearly both the proposed itinerary and number of miles, the system tells you that you don't have enough miles and clears the search. Very frustrating....