[Ken Maltby]

What is your PC's OS? What program is saying "invalid file name"? What "Launcher" program are you using?

I use the USB enable function of the Kobo Start Menu (KSM7) to make a USB connection to my win 7 machine. That puts two new drive letters in windows explorer, one for the internal uSD card and one for the external uSD card. The internal card is labled KOBOeReader (L:), the external one is labled Removable Disk (M:). I copy over files to my hidden folder by just drag&drop.

I have the Kobo plugins disabled in calibre, so "calibre cannot detect devices that are managed by disabled plugins." So the device doesn't show, in caliber, when I make the USB connection.

You can make your hidden folder a device in caliber, though. Then calibre will build its file/folder structure there, from any existing books there, and will add to it as you send books to the folder device. This is one way to interface KOReader with calibre and your Kobo device, using the USB cable.

There are also wireless ways to connect to calibre. You can "pull" files from calibre using the OPDS function of KOReader. (The simplest way to move one book at a time, IMHO.) You can also "Push" books to your device from calibre, using KOReader's "Calibre wireless connection" function.

Luck;
Ken