1. It had never happened in recent past and every time I used to mount the share folder for the guest OS in virtual box it used to happen vide this command :
sudo mount.vboxsf sharedfolder /mnt/foldername
where sharedfolder is the new folder you have created inside guest OS home directory in virtual box ~ ie /home to be mounted with another folder from host OS as foldername here
but today it showed an error with the following message :
/sbin/mount.vboxsf mounting failed with the error protocol error
as seen below :
tried everything around with the commands but didn't get resolved before I attempted to do the more simpler thing of going to the pwd of the folder where I created it to be mounted and typed the same command without path
surprisingly it worked!!!!