The Elevation inflation factor cannot be estimated because the input points contain areas where each point has the same measured value. Some variability in the measured values is required in each subset to estimate the elevation inflation factor.
Type a value into the Elevation inflation factor parameter. To determine an appropriate value, select some of your input points that do not have constant values and note the elevation inflation factor that Empirical Bayesian Kriging 3D estimates.
Alternatively, increasing the Subset size may resolve the error.