A couple of ideas found on Cisco forums, [url]https://supportforums.cisco.com/thread/2033218[/url]:
[SIZE=12px][FONT=Arial][COLOR=#333333]Do you have a Layer 3 interface (interface vlan 73) on the 3750? Please try[/COLOR][/FONT][/SIZE][FONT=Arial][COLOR=#333333][SIZE=12px]the following on the leaf switch:[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px] [/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]ip routing[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px] [/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]interface vlan 73[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]ip helper-address[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]exit[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px] [/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]service dhcp[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px] [/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]2. try to use encapsulation on both ports[/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px] [/SIZE][/COLOR][/FONT]
[FONT=Arial][COLOR=#333333][SIZE=12px]switchport trunk encapsulation dot1q[/SIZE][/COLOR][/FONT]