Solved! Go to Solution.
I think you should submit an IR for this. In NX 11 there was a project to change the behavior of sketch plane definition. Before, the system used to create an intermediate datum csys (internal to the sketch) onto which the sketch was attached. From NX 11, that is no longer the case. This seems to have altered the behavior compared to previous versions of NX. In NX 10 and prior versions, the error message does not occur.