I use two external drives for backups Ghost knows about each. But about one in four times when I plug in a drive and then launch Ghost to make the backup, Ghost reports that the other drive is plugged in and I thus can't make a backup. Windows 7 (my OS) however always correctly reports which drive is plugged in. So it's like Ghost doesn't bother to ask the OS about the drive identify but instead relies on something else, which isn't always correct.
Unplugging the drive and plugging it back in doesn't help. Killing and relaunching the Ghost processes doesn't seem to help either. The only solution I have so far is to reboot the computer. Right after that, Ghost does identify the external drive correctly and I can proceed to make my backup. But after maybe four backups, switching drives each time, Ghost then gets it wrong again.
My apologies if this has been addressed elsewhere - I couldn't find it.