Dear gPPI Users,
I am running into the same problem that Theresa outlined - using a sphere that is outside the mask for very few subjects. I have followed Donald's instructions and set equalroi: 0, but the estimation stops anyway. I am not sure why this is happening and would love some advice. Here my P structure:
P =

subject: 'C09_20090402'
VOI: '/Volumes/.../AntInsula_-21_23_-8_mask.nii'
Region: 'AntInsula_-21_23_-8'
SPMver: 8
directory: '/Volumes/.../FLM_LinearPDerivatives_simple/'
Estimate: 1
contrast: {'Omnibus F-test for PPI Analyses'}
extract: 'mean'
Tasks: {'1' 'All'}
Weights: []
maskdir: []
equalroi: 0
FLmask: 0
VOI2: {}
analysis: 'psy'
method: 'cond'
CompContrasts: 1
Weighted: []
Contrasts: [1x2 struct]

Here the output:
Log File: C09_20090402_PPPI_12_13_2013_2.log

PPPI Version: 7.12.4-10-2013
Parameters used:
Processing subject: C09_20090402
VOI file : /Volumes/.../AntInsula_-21_23_-8_mask.nii
Output file will be: C09_20090402_AntInsula_-21_23_-8_session#_cond_PPI_regressors.txt
Contrast : Omnibus F-test for PPI Analyses
Analysis : Psychophysiological Interactions
Extraction : mean
Tasks : _1_All
Method : Condition Specific
VOI has 94762 voxels in 3x3x3 space
VOI has 33 voxels in 3x3x3 space. This is in the the same space as the input data and functional mask.
Failed: C09_20090402