DF1 is a protocol that only supports PCCC style addressing, such as N7:0. In order to use PCCC commands with a ControlLogix, you must use the PLC/SLC Mapping feature in RSLogix5000.
To do this, in RSLogix 5000 you would create an array of INT and name the array N7. Then go to Logic->Map PLC/SLC Messages and create a map pointing to file 7 and set the tag to N7
This will now make the processor accept and respond to PCCC (DF1) messages that read/write to the N7 file.
This is only a limitation with DF1. If using the EthernetIPforCLXCom driver, you can directly access any of the tags by name.