i got he same problem my nokia is on mass storage and could work properly due to the wpd file system error well.. by trial an error i came with a solution so forget about the driver
of wpd file system
open computer management by right click on
1. my computer - manage
2. disk management - select your portable storage
3. right click and select change drive letter and paths..
4. add and tick on assign the following drive letter (any letter u wish for..) and OK it will allow you to open and used ur portable storage.. and the WPD file system storage will still remain with the exclamation symbol! :P