Im not sure if this will help anyone, but this is how i have managed to get my drives to map properly.
First, let me lay down some facts/specs,
Laptop, vista 32bit. Admin account / User account - different names/passwords.
DS409+ totally different login name/password to windows accounts - DynDNS mapped. RAID 5.
Mapped to five shared folders on the DS409+ volume
I tried the synology assistant utility to map the drives, but I got the "unable to reconnect mapped drives" balloon on startup.
So, i goto "computer" see the unmapped drives, open one, get password login (with no options to save password) Enter DS login and done, can view that folder. However, I can now view all folders (the remaining 4) so once each folder has been opened once they show up properly in "computer" (without the big red X)
So, this wasn't quite what I wanted. My solution was the following.
Deleting all mapped folders pointing to the DS409+.
Going to "
computer"
Clicking "
Map Network Drives" You get this.

Choose your drive, as per normal, upon clicking the browse button to locate your DS, you will need to enter your
login creds for your DS, make sure "
reconnect at logon" is ticked. Then click on "
connect using different username" Here enter the DS login creds that you want to use to connect to the DS with. (
can be admin or user or any other group as long as the account is held on the DS)
click "finish" and your done, continue to map as many drives as you need.