Since I am a windows user I got the Virtualbox version of FreeSurfer and to use fs fast, I installed Octave on the virtual machine, I set the environment variables and then when I run the command

selxavg3-sess -analysis rtopy.lh -sf sessid

which runs a retinotopy analysis, I get the following error:

sxa3pwd = /usr/local/freesurfer/projects/retinotopy_xxx

sxa3cmd = /usr/local/freesurfer/fsfast/bin/selxavg3-sess -analysis rtopy.lh -sf sessid

error: `fast_fileexists' undefined near line 5 column 4

------------------------------------------

ERROR: fast_selxavg3() failed\n

Any idea of the cause of this error and how to run around?

Thank you,