Unidentifiable model in lmer

To: r-sig-mixed-models at r-project.org
From: taka.6765 at gmail.com
Date: Thu, 17 Sep 2015 17:52:56 -0400
Subject: [R-sig-ME] Unidentifiable model in lmer

Hi everyone,

I have been working on a linear mixed effect model by using lmer() 
function, but I got an error saying that the fitted model is not 
identifiable.

The data set includes the following variables:
y = a numeric variable
factorA = a 3-level categorical variable
factorB = a 2-level categorical variable
subjectID = subject id number. 2 measurements of y for each subject

R code and output are as follows:

 > (result <- lmer(y ~ factorA + factorB + factorA*factorB + 

(1|subjectID)))
Linear mixed model fit by REML ['merModLmerTest']
Formula: y ~ factorA + factorB + factorA * factorB + (1 | subjectID)
REML criterion at convergence: 1928.966
Random effects:
  Groups    Name        Std.Dev.
  subjectID (Intercept) 4711
  Residual              7688
Number of obs: 97, groups:  subjectID, 51
Fixed Effects:
       (Intercept)           factorA1           factorA2 factorB1 
factorA1:factorB1  factorA2:factorB1
             62411              -2700              -1124 
-1037               1279               2482

 > summary(result)

Model is not identifiable...
summary from lme4 is returned
some computational error has occurred in lmerTest
Linear mixed model fit by REML ['lmerMod']
Formula: y ~ factorA + factorB + factorA * factorB + (1 | subjectID)

REML criterion at convergence: 1929

Scaled residuals:
      Min       1Q   Median       3Q      Max
-1.93423 -0.62611  0.01837  0.48887  2.73380

Random effects:
  Groups    Name        Variance Std.Dev.
  subjectID (Intercept) 22194074 4711
  Residual              59108495 7688
Number of obs: 97, groups:  subjectID, 51

Fixed effects:
                   Estimate Std. Error t value
(Intercept)          62411       2065  30.227
factorA1             -2700       3238  -0.834
factorA2             -1124       3008  -0.374
factorB1             -1037       2512  -0.413
factorA1:factorB1     1279       4013   0.319
factorA2:factorB1     2482       3642   0.681

Correlation of Fixed Effects:
             (Intr) fctrA1 fctrA2 fctrB1 fA1:B1
factorA1    -0.638
factorA2    -0.687  0.438
factorB1    -0.608  0.388  0.418
fctrA1:fcB1  0.381 -0.601 -0.262 -0.626
fctrA2:fcB1  0.420 -0.268 -0.606 -0.690  0.432

 >

Could anyone give me some idea of why this unidentifiability problem 
happens and how to fix it?
Any help would be appreciated.

Best regards,
Takahiro