title: zeroinfl model - Warning message: In sqrt(diag(object$vcov)) : NaNs produced
body: <p>I'm trying to run zero-inflated negative binomial but I'm coming across a &quot;NaNs produced&quot; warning when checking the model that prevents me from seeing outcomes. Here's some mock data that's a simplified version of my actual data - my real data has many more observations per species + more species:</p>
  <pre><code>df1 &lt;- data.frame(species = c(&quot;Rufl&quot;,&quot;Rufl&quot;,&quot;Rufl&quot;,&quot;Rufl&quot;,&quot;Assp&quot;,&quot;Assp&quot;,&quot;Assp&quot;,&quot;Assp&quot;,&quot;Elre&quot;, &quot;Elre&quot;,&quot;Elre&quot;, &quot;Elre&quot;,&quot;Soca&quot;,&quot;Soca&quot;,&quot;Soca&quot;,&quot;Soca&quot;),
                    state = c(&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;,&quot;warmed&quot;,&quot;ambient&quot;),
                    p_eaten = c(0, 0, 3, 0, 0, 1, 15, 0, 20, 0, 0, 2, 0, 3, 87, 0))
  </code></pre>
  <p>Here's the model I'm attempting to run, with an interaction between state and species:</p>
  <pre><code>library(pscl)
  mod1 &lt;- zeroinfl(p_eaten ~ state * species,
                       dist = 'negbin',
                       data = df1)
  summary(mod1)
  </code></pre>
  <p>This is when I get <code>Warning message: In sqrt(diag(object$vcov)) : NaNs produced</code>. How can I fix this warning message so that I'm able to see model outcomes? Thanks!</p>
  <p>Using R version 4.0.2, Mac OS X 10.13.6</p>