problems with robust Mahalanobis distances in robust regression

Question

I use lmrob from robustbase and this is what I get once I try to plot residuals "plot(Model, which = c(1))".

In robMD(x = if (!is.null(x[["x"]])) x$x else if (!is.null(x[["model"]])) model.matrix(x, : Failed to compute robust Mahalanobis distances, reverting to robust leverages.

I am not sure how to proceed or if I can simply reply on robust leverages

thanks