This can be caused due to a variety of things: they all boil down to the error message encountered when attempting to submit the file.
Error 7.1.7 is the main reason you may not be able to select a victim - offender relationship
This error states that
Victim - Offender Relationship cannot be entered unless the Victim is connected to at least one UCR Offense Code that is considered a Crime Against Person or at least one Robbery:
“09A” (Murder and Non-Negligent Manslaughter)
“09B” (Negligent Manslaughter)
“09C” (Justifiable Homicide)
“100” (Kidnapping/Abduction)
“11A” (Rape)
“11B” (Sodomy)
“11C” (Sexual Assault with an Object)
“11D” (Fondling)
“13A” (Aggravated Assault)
“13B” (Simple Assault)
“13C” (Intimidation)
“36A” (Incest)
“36B” (Statutory Rape)
“64A” (Human Trafficking – Commercial)
“64B” (Human Trafficking – Involuntary)
“120” (Robbery)
You may only select a victim-offender relationships for the codes listed above. Any other code will not allow you to select a relationship due to the victim not being an individual or LEO. To resolve this error, change the UCR code to the one that best relates to your case.
Another error message that will prevent you from selecting a victim-offender relationship is 7.1.IN1
This error message is given when there are too many victim-offender relationships.
To resolve this error you must proceed with 10 or fewer relationships per victim. NIBRS does not allow more.