This message means that you have unconstrained DOF in the model. To properly constrain the features of a part, establish a predominant datum reference frame (DRF) that can constrain all degrees of freedom (DOF) of the part. Parts generally require a predominant datum reference frame that constrains all 6 DOF. An exception is when a part is symmetrical, such as a simple sphere or a simple cylinder. In these cases, there may be degrees of freedom left unconstrained in the predominant DRF because they are not required to define the part
Generally you select the part features that orient or locate the part in an assembly as the predominant reference frame. Those features should be the first features in your model.