[R] Failure to run mcsamp() in package arm

[Michael Kubovy]

Dear r-helpers,

I can run the examples on the mcsamp help page. For example:
****************************************
 > M1 <- lmer (y1 ~ x + (1|group))
 > (M1.sim <- mcsamp (M1))
fit using lmer,
3 chains, each with 1000 iterations (first 500 discarded)
n.sims = 1500 iterations saved
                           mean  sd 2.5%  25%  50%  75% 97.5% Rhat n.eff
beta.(Intercept)           0.1 0.7 -1.2 -0.3  0.1  0.5   1.4  1.0  1500
beta.x                     2.5 0.4  1.7  2.2  2.5  2.7   3.2  1.0  1500
sigma.y                    3.8 0.3  3.3  3.6  3.7  3.9   4.3  1.0    61
sigma.grop.(In)            1.5 0.8  0.0  1.0  1.4  1.9   3.3  1.4    12
eta.group.(Intercept)[1]   0.0 1.0 -2.1 -0.5  0.0  0.6   2.0  1.0  1500
eta.group.(Intercept)[2]   1.0 1.1 -0.9  0.2  0.9  1.7   3.4  1.0    59
eta.group.(Intercept)[3]  -1.3 1.2 -4.0 -2.0 -1.3 -0.4   0.5  1.0    66
eta.group.(Intercept)[4]   1.3 1.1 -0.6  0.4  1.1  2.0   3.7  1.1    43
eta.group.(Intercept)[5]  -0.7 1.0 -3.0 -1.4 -0.6  0.0   1.2  1.0   120
eta.group.(Intercept)[6]   1.5 1.2 -0.3  0.6  1.4  2.2   4.0  1.0    49
eta.group.(Intercept)[7]   0.3 1.0 -1.7 -0.3  0.1  0.8   2.5  1.0   440
eta.group.(Intercept)[8]  -1.6 1.2 -4.0 -2.4 -1.5 -0.6   0.3  1.1    41
eta.group.(Intercept)[9]   0.4 1.0 -1.6 -0.2  0.2  0.9   2.7  1.0   180
eta.group.(Intercept)[10] -1.0 1.1 -3.3 -1.6 -0.9 -0.2   0.8  1.0    86

For each parameter, n.eff is a crude measure of effective sample size,
and Rhat is the potential scale reduction factor (at convergence,  
Rhat=1).
****************************************
But when I try to do this with my own data I get an error:
****************************************
 > display(e7.lmer2)
lmer(formula = baLO ~ I(baRatio - 0.985) + delta + (1 + I(baRatio -   
0.985) + delta | subject), data = e7)
                    coef.est coef.se
(Intercept)        -0.19     0.06
I(baRatio - 0.985) -4.95     0.74
delta               0.41     0.06
Error terms:
Groups   Name               Std.Dev. Corr
subject  (Intercept)        0.13
           I(baRatio - 0.985) 2.57      0.45
           delta              0.22     -0.12 -0.94
Residual                    0.39
number of obs: 494, groups: subject, 13
deviance = 551.4

 > e7.sim <- mcsamp(e7.lmer2)
Error in as.bugs.array(sims, program = "lmer", n.iter = n.iter,  
n.burnin = n.burnin,  :
	error in parameter sigma. in parameters.to.save
****************************************
I would appreciate a pointer to what the problem might be.
_____________________________
Professor Michael Kubovy
University of Virginia
Department of Psychology
USPS:     P.O.Box 400400    Charlottesville, VA 22904-4400
Parcels:    Room 102        Gilmer Hall
         McCormick Road    Charlottesville, VA 22903
Office:    B011    +1-434-982-4729
Lab:        B019    +1-434-982-4751
Fax:        +1-434-982-4766
WWW:    http://www.people.virginia.edu/~mk9y/