title: Error in summary quantreg backsolve
body: <p>When I run a quantile regression in R, using the <code>quantreg</code> package, and then I run <code>summary(quantregObject)</code>, I get this error message:</p>
  
  <blockquote>
    <p>Error in base::backsolve(r, x, k = k, upper.tri = upper.tri, transpose = transpose, : singular matrix in 'backsolve'. First zero in diagonal [1]</p>
  </blockquote>
  
  <p>Any suggestion how could I fix this problem?</p>