That isn't an error message, that is just a choice; users can use either the "bash" or "tcsh" shell. This doesn't affect running AFNI; there is just a different style of syntax for setting variables, for example:
# in tcsh: use keyword "set", and can have spaces
set a = 20
echo $a
# in bash: no keyword, can*not* have spaces
a=20
echo $a
To know which shell you are currently using, you can type:
echo $0
If you really want to change to tcsh as default, doing so in Linux is described in the install instructions here:
[
afni.nimh.nih.gov]
(In Mac, some different steps are necessary.)
--pt