It indicates that Z-Axis Delay has been enabled in the design on a higher tier, namely Allegro PCB Designer w/High Speed Option.
Z-Axis delay functionality will add the depth (distance) the signal travels down the via or pins holes when checking for length/delay calculations which is not supported in OrCAD PCB Designer Professional.
If you want to include the Z-Axis delay functionality then you need to open the design using Allegro PCB Designer w/High Speed Option license. If you have no plans on adding in the Z-Axis to the delay calculations then you can turn it off using Setup > Constraint > Modes under the Electrical Options category (using Allegro PCB Designer w/High Speed Option license) or on the lower tier license select the Update to Tier button under the Tiering tab of File > Properties.
Hope this helps,