SanDIsk Cruzer 16GB V3 upgrade problem

I have a sandisk cruzer 16GB with V2 secure access  and acidentally clicked on the V3 upgrade notification without first copying  the files from the secure access vault to my PC.  On realising ths I hit the cancel button part way through the upgrade in panic and now I cannot access the files on the flash drive as I am getting the following error message:

“Not allow to add file in the FileSystem root”

How can I recover the files please?