Most systems are case sensitive.
CD aSubFolder(no slash). Yup, trying to remember my ms-dos...
Active session:  SFTPxxxx@00.00.000:23
Error changing directory to '/aSubFolder'.
No such file or directory.
Error code: 2
Error message from server: No such file
cd ../aSubFolder(trying to remember my MS-DOS specifics).
CDdescription is pretty straight forward...