title: Error in MEEM(object, conLin, control$niterEM) : Singularity in backsolve at level 0, block 1... Linear mixed model, nlme, R
body: <pre class="lang-r prettyprint-override"><code>m1 =lme(fixed=Hour~Age*Ethnicity*GHUsedFlag*Disability,
     random=~Age|Id, data=mydf)
  </code></pre>
  <p>In my model I am checking multi level interactions. Age- numeric repeated measure, Ethnicity- character factor, GHUsedFlag- logical, Disability- Character- factor , Hour- numeric, outcome variable.
  I am getting this error when introduced <code>Disability</code> in the model. Can not really understand why is error is occurring and how to counter it. Any help is appreciated.
  I am using nlme package in R.</p>
  <blockquote>
  <p>Error in MEEM(object, conLin, control$niterEM) :
  Singularity in backsolve at level 0, block 1</p>
  </blockquote>