Thanks to you both. I can't seem to find the error here despite much work, having done both of the suggested steps here.

In case it was an issue of not having a column with data, I added the path to the data in the covariates file, but did nothing except changed the error a bit to include the Fatal Signal 11 at the end.

My error remains:
++ 3dttest++: AFNI version=AFNI_2011_12_21_1014 (Nov 2 2015) [64-bit]
++ Authored by: The Bob++
++ 217793 voxels in -mask dataset
++ Covariates file: 4 columns, each with 496 rows
+ Covariate column labels: subject;age;gender;Z_score
+ Found 2 numeric columns: age gender
+ Found 1 dataset name column: Z_score
++ loading covariates
100408' in covariates file '
101006' in covariates file '
101107' in covariates file '

(etc through 496 lines)

Fatal Signal 11 (SIGSEGV) received
THD_delete_3dim_dataset
3dttest++ main
Bottom of Debug Stack
** AFNI version = AFNI_2011_12_21_1014 Compile date = Nov 2 2015
** [[Precompiled binary macosx_10.7_Intel_64: Nov 2 2015]]
** Program Death **

When I used the DAFNI_DEBUG_TABLE I got this output:

++ Mixed Table: processing file Philip_covar_11_12.txt
+ first line = 'subject age gender Z_score'
+ found 4 labels in first line
+ processing row #0 = '100307 27 1 /Volumes/Faraday/DATA/DBS_RSFC/100307/R_vent.100307.Z+tlrc '
+ deciding format of 3 columns
+ -- col#1 is numeric
+ -- col#2 is numeric
+ -- col#3 is string
+ processing row #1 = '100408 33 0 /Volumes/Faraday/DATA/DBS_RSFC/100408/R_vent.100408.Z+tlrc '
+ processing row #2 = '101006 35 1 /Volumes/Faraday/DATA/DBS_RSFC/101006/R_vent.101006.Z+tlrc '
+ processing row #3 = '101107 22 0 /Volumes/Faraday/DATA/DBS_RSFC/101107/R_vent.101107.Z+tlrc '


<AFNI_table
ni_type="String,2*float,String"
ni_dimen="496"
Labels="subject;age;gender;Z_score" >
"100307" 27 1 "/Volumes/Faraday/DATA/DBS_RSFC/100307/R_vent.100307.Z+tlrc"
"100408" 33 0 "/Volumes/Faraday/DATA/DBS_RSFC/100408/R_vent.100408.Z+tlrc"
"101006" 35 1 "/Volumes/Faraday/DATA/DBS_RSFC/101006/R_vent.101006.Z+tlrc"
"101107" 22 0 "/Volumes/Faraday/DATA/DBS_RSFC/101107/R_vent.101107.Z+tlrc"
(etc)


I'm using a mac OS 10.9.5, bluefish editor (also used textmate editor, in case that was the issue, but both yield the same results. Any further advice would be appreciated. I would be happy to email my covariates and command files somewhere if that's at all helpful.