mkdir: cannot create directory : Protocol error : Virtualbox Shared folder

Question

I am trying to create folders and file in Virtualbox shared folder from Host to guest. But i get this error mkdir: cannot create directory : Protocol error.

Below are steps i performed to share folder
1:My host OS is Ubuntu and my guest is Ubuntu.

2:I attached a share folder to virtualBox VM 
  Folder Path:/DR/vault/config 
  Folder:config selected automount and make permanent.

3:In Guest OS i installed virtualbox guest additions

4:I am trying to mount folder on /mount/config path
  I added entry in guest's /etc/fstab as 
  /config         /mount/config  vboxsf  rw,uid=1000,gid=1000      0       0

Path gets successfully mounted after Guest reboot also i can see the files created in /DR/vault/config(Guest) to /mount/config(Guest) but i cant create folder or file in /mount/config (Guest)

Please suggest if anything is missing or if there is any other way.