i try mount VB shared filder (host is windows) 

```
mount -t vboxsf share ~/host
/sbin/mount.vboxsf: mounting failed with the error: Protocol error

```

1) the operating systems on both host and guest machine 
Host : windows 7
Guest : debian 

2) How you are sharing the folder.
i setup it on Devices/shared folders settings - virtualbox configuration. 
i setup E:/ as Tansient Folder 

3) Have you installed Virtual Box Guest Additions on the guest? 
yes

4) Which version of virtual box you are using 
4.3.8

5) Have you installed the Virtual Box extension pack from their website? We need more information to be able to help.

i not install extension pack, only from menu quest additions then in virtual debian as root install it.