39 - DATE OF SERVICE:
The date of service is: (a) invalid or blank or (b) more than one year from date of birth (newborn) or (c) in conflict with the explicit modifier indicated.
This one is pretty self-explanatory. As an example, if a weekend premium modifier is used the service date needs to be on a weekend, or if billing a fee modifier such as L40 on a patient outside the corrected age range.