When in the File | Open window, to open a file, the mapped drive has a question mark next to it and is not able to be accessed. If the question mark is not there, the way the mapped drive is listed is different than outside of Toad, in the Windows Explorer. There is not problem accessing the drive on the same machine using Windows Explorer.
Here is a message that is giving when clicking on the drive. In this example, it is the G: drive.
"G:\ is unavailable. If the location in on this PC, make sure the device or drive is connected or the disc is inserted, and then try again. If the location is on a network, make sure you're connected to the network or Internet, and then try again. If the location still can't be found, it might have been moved or deleted."