title: Error in R: multi effects models
body: <p>I'm having a few issue's I'd appreciate some help with.</p>
  
  <pre><code> head(new.data)
    WSZ_Code Treatment_Code Year Month TTHM CL2_FREE      BrO3 Colour  PH  TURB seasons
  1        2              3 1996     1 30.7     0.35 0.5000750   0.75 7.4 0.055  winter
  2        6              1 1996     2 24.8     0.25 0.5001375   0.75 6.9 0.200  winter
  3        7              4 1996     2 60.4     0.05 0.5001375   0.75 7.1 0.055  winter
  4        7              4 1996     2 58.1     0.15 0.5001570   0.75 7.5 0.055  winter
  5        7              4 1996     3 62.2     0.20 0.5003881   2.00 7.6 0.055  spring
  6        5              2 1996     3 40.3     0.15 0.5003500   2.00 7.7 0.055  spring
  
          library(nlme)
      &gt; mod3 &lt;- lme(TTHM ~ CL2_FREE, random= ~ 1| Treatment_Code/WSZ_Code, data=new.data, method ="ML")
      &gt; mod3
      Linear mixed-effects model fit by maximum likelihood
        Data: new.data 
        Log-likelihood: -1401.529
        Fixed: TTHM ~ CL2_FREE 
      (Intercept)    CL2_FREE 
         54.45240   -40.15033 
  
      Random effects:
       Formula: ~1 | Treatment_Code
              (Intercept)
      StdDev: 0.004156934
  
       Formula: ~1 | WSZ_Code %in% Treatment_Code
              (Intercept) Residual
      StdDev:    10.90637 13.52372
  
      Number of Observations: 345
      Number of Groups: 
                    Treatment_Code WSZ_Code %in% Treatment_Code 
                                 4                            8 
      &gt; plot(augPred(mod3))
      Error in plot(augPred(mod3)) : 
        error in evaluating the argument 'x' in selecting a method for function 'plot': Error in sprintf(gettext(fmt, domain = domain), ...) : 
        invalid type of argument[1]: 'symbol'
  </code></pre>
  
  <p>I'm not sure why I get this error. The ranef plot seems OK</p>
  
  <pre><code>plot(ranef(mod3))
  </code></pre>
  
  <p>But that only gives the value of the random intercepts, no TTHM predictions. 
  I'm looking for a way to plot the predictions like in a typical augPred which would show all the random effects for each zone. Hope that makes sense.</p>