It is possible that the Darkroom closes itself when you are at the stage of purchasing photos. The software closes during the progress bar. 

Before importing the photos again, check your online account on  

Once logged in to your account, select My Purchased HDR Photos from the left-hand menu. 

Check to see if your photos are present by selecting the import date. 

If your photos are present, you can select them all using the brackets and upload the selection.