Strange, should be some weird mixup with those drivers and the Toshiba notebook. Quick explanation anyway, Windows automaticly installs a simplistic driver for your videocard when you allow it to surf for it. In general that driver can sometimes cause minor performance drops for your videocard and that's what we are trying to avoid here.
Anyhow, the driver made specifically for your notebook can be found
here. I wanted to enter all details for you but it gave me the option for 4 types of the a 100. I doubt that will be much of an issue with just the videocard but I'm just trying to avoid any issues here.
If this still doesn't work (which I highly doubt), then do what Windows asks and install the driver on top off that.