Dot indexing error in BATCH

To whom it may concern, 

I am writing a script in MATLAB to run an analysis in CONN toolbox, using BATCH commands. In there, I set up some commands to do the appropriate preprocessing steps:

BATCH.Setup.Preprocessing.overwrite='No';
BATCH.Setup.Preprocessing.done=1;
BATCH.Setup.Preprocessing.voxelsize_anat=0.8;
BATCH.Setup.Preprocessing.voxelsize_func=2;
BATCH.Setup.Preprocessing.fwhm=6;

When I try to run this script on a small subset of my real dataset, I keep getting the following error:

"Unable to perform assignment because dot indexing is not supported for variables of this type.

Error in Batch_all_subjects (line 46)
BATCH.Setup.Preprocessing.overwrite='No';"

If I then comment out line 46, the same error will repeat with the next line. 

I do not understand why this error would appear at this line, as I'm not even defining variables in this line. 
Any help would be much appreciated. 

Kind regards, 
Romke Hannema