Possible Clues:

• ''Sorry, we're full''
• Space observation
• Meaning of an unlit "vacancy" sign
• What there was at the inn
• Bad news at the inn
• Bad news when arriving at a 44-Down
• 'We can't squeeze any more in'
• ''We're full!''
• Lack of space to fasten the boat on back here
• Nativity inn problem