Not sure if it was necessary, but it didn't work for me until I used lowercase for the VirtualBox name of the shared folder (the folder itself was still capitalized).
su root
mount -t vboxsf -o uid=ben,gid=ben,umask=022 notes /home/ben/Notes
exit
That is what worked, here are some things that didn't work, for this folder only
virtualbox shared folder location in guest machine
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