  We extend the methods of Davis-Januszkiewicz-Lafont to provide a new
obstruction to smooth Riemannian metric with non-positive sectional curvature.
We construct examples of locally CAT(0) 4-manifolds $M$, whose universal covers
satisfy isolated flats condition and contain 2-dimensional flats with the
property that $\sqcup\ \partial^\infty F_i \hookrightarrow \partial^\infty
\tilde M$ are non-trivial links that are not isotopic to any great circle link.
Further, all the flats in $\tilde M$ are unknotted at infinity, and yet $M$
does not have a Riemannian smoothing.
