I successfully ran ICC(3,1) with a GM mask based on TT_N27 covering the whole brain.

I had issues running ICC(2,1) with a mask covering amygdala and fusiform gyrus.

sub-brik 11contains t-stat for a contrast of interest:

#!/usr/bin/env tcsh
3dICC -prefix ICC2_N40_amyIT. -jobs 2 \
-model '1+(1|session)+(1|Subj)' \
-mask amy.IT_mask.+tlrc. \
-dataTable \
Subj session InputFile \
s1 one 3051.FP.stats.VAL.GLT.+tlrc'[11]' \
s1 two 3051.SP.stats.VAL.GLT.+tlrc'[11]' \
s2 one 3052.FP.stats.VAL.GLT.+tlrc'[11]' \
s2 two 3052.SP.stats.VAL.GLT.+tlrc'[11]' \
s3 one 3055.FP.stats.VAL.GLT.+tlrc'[11]' \
s3 two 3055.SP.stats.VAL.GLT.+tlrc'[11]' \
s4 one 3061.FP.stats.VAL.GLT.+tlrc'[11]' \
s4 two 3061.SP.stats.VAL.GLT.+tlrc'[11]' \
.
.
.
.


Output:
Reading input files now...

Reading input files for effect estimates: Done!

Loading required package: lme4
Loading required package: Matrix
If the program hangs here for more than, for example, half an hour,
kill the process because the model specification or something else
is likely inappropriate.

[1] "Great, test run passed at voxel (21, 25, 20)!"
Error in asMethod(object) : not a positive definite matrix
Calls: nrow ... asMethod -> as -> .class1 -> as -> asMethod -> as -> asMethod
Execution halted


Thank you,
ns