Hi, I am seeking help with an error when running the example from R
Documentation for TukeyHSD.  The error occurs with any example I run, from
any text book or website.  thank you...

> plot(TukeyHSD(fm1, "tension")).
Error in plot(confint(as.glht(x)), ylim = c(0.5, n.contrasts + 0.5), ...) :
  error in evaluating the argument 'x' in selecting a method for function
'plot': Error in UseMethod("vcov") :
  no applicable method for 'vcov' applied to an object of class "NULL"


> ?TukeyHSD
> require(graphics)

> summary(fm1 <- aov(breaks ~ wool + tension, data = warpbreaks))
            Df Sum Sq Mean Sq F value  Pr(>F)
wool         1    451   450.7   3.339 0.07361 .
tension      2   2034  1017.1   7.537 0.00138 **
Residuals   50   6748   135.0
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
> TukeyHSD(fm1, "tension", ordered = TRUE)
  Tukey multiple comparisons of means
    95% family-wise confidence level
    factor levels have been ordered

Fit: aov(formula = breaks ~ wool + tension, data = warpbreaks)

$tension
         diff        lwr      upr     p adj
M-H  4.722222 -4.6311985 14.07564 0.4474210
L-H 14.722222  5.3688015 24.07564 0.0011218
L-M 10.000000  0.6465793 19.35342 0.0336262

> plot(TukeyHSD(fm1, "tension"))
Error in plot(confint(as.glht(x)), ylim = c(0.5, n.contrasts + 0.5), ...) :
  error in evaluating the argument 'x' in selecting a method for function
'plot': Error in UseMethod("vcov") :
  no applicable method for 'vcov' applied to an object of class "NULL"
>
> sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: i386-pc-mingw32/i386 (32-bit)

attached base packages:
 [1] grid      tcltk     splines   stats     graphics  grDevices datasets
 utils     methods   base

other attached packages:
 [1] RcmdrPlugin.HH_1.1-30 HH_2.2-30             latticeExtra_0.6-19
RColorBrewer_1.0-5
 [5] leaps_2.9             multcomp_1.2-12       mvtnorm_0.9-9992
 NADA_1.5-4
 [9] ggplot2_0.9.0         Rcmdr_1.8-3           car_2.0-12
 nnet_7.3-1
[13] DAAG_1.12             survival_2.36-12      randomForest_4.6-6
 rpart_3.1-52
[17] RODBC_1.3-5           tree_1.0-29           spatstat_1.25-5
mgcv_1.7-13
[21] sciplot_1.0-9         spdep_0.5-45          coda_0.14-6
deldir_0.0-16
[25] maptools_0.8-14       foreign_0.8-49        nlme_3.1-103
 MASS_7.3-17
[29] boot_1.3-4            sp_0.9-98             odesolve_0.9-9
 mcmc_0.8
[33] lme4_0.999375-42      Matrix_1.0-6          lattice_0.20-6
 chron_2.3-42
[37] akima_0.5-7           rcom_2.2-3.1.1        rscproxy_1.3-1

loaded via a namespace (and not attached):
 [1] colorspace_1.1-1 dichromat_1.2-4  digest_0.5.2     memoise_0.1
 munsell_0.3      plyr_1.7.1
 [7] proto_0.3-9.2    reshape2_1.2.1   scales_0.2.0     stats4_2.15.0
 stringr_0.6      tools_2.15.0

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