title: hw() function in R doesn't work properly on my laptop only
body: <p>I'm studying time series and need to use hw() function. I cannot make it working even on a simple code based on the co2 dataset :</p>
  <pre><code>library(forecast)
  co2_train=window(co2,start=c(1959,1),end=c(1989,12))
  co2_test=window(co2,start=c(1990,1),end=c(1997,12))
  h=hw(co2_train,seasonal='additive',damped=FALSE,h=96) #code stops to be executed here
  accuracy(h)
  </code></pre>
  <p>When I load the R Markdown, the first time I try to run it I get the following error :</p>
  <blockquote>
  <p>Error in ets(x, &quot;AAA&quot;, alpha = alpha, beta = beta, gamma = gamma, phi = phi, :
  No model able to be fitted</p>
  </blockquote>
  <p>Then if I re-run the code, RStudio is compiling indefinitively and I need to restart it to work again. All other models are working (ARIMA, Neural networks forecast...). Only this function makes trouble.</p>
  <p>I tried to create a new file, a new project, restart R Studio, reinstall R Studio... with no luck.</p>
  <p>Any help on this would be very appreciated.</p>
  <p>Thanks.</p>