This message indicates that the a delivery method is not available. For example, if your only delivery method was mail and a mail delivery method was blocked two days before the event, your patrons will receive this message if they are purchasing tickets two days before the event.

Here are instructions on how to correct this: 
  1. Go to Tickets
  2. Under Configuration, click Sales methods.
  3. Click Online Sales, go to the Delivery Methods Tab. 
  4. See which delivery method is the default method.
  5. Go to Tickets > click Delivery methods under Configuration.
  6. Click on the delivery method that was marked as default for Online Sales.  
  7. Click Edit delivery method under Tasks.  See if the box to Block this delivery method is marked.  If so, either unmark this option so the delivery method can be used up until the start time of the event OR if this is correct, go back to Tickets > Delivery Methods and click Add to add a new method.  In the new method, do not mark the box to block this delivery method.
  8. Then go to Tickets > Sales Methods > online sales.  Go to the Delivery methods tab.
  9. Click Add and add the new delivery method and mark the box to Set as default delivery method.
  10. Click Save.