Twain Problem (Windows XP Home)

I am using Twain 5 to run my Epson scanner under my Administrator account.
If I try to use Twain under the "Guest" or a limited "Named" account, with
the Administrator logged off, it fails to run, with a message that the
device can't be found. It does work, though, with these accounts if the
Administrator is logged on.

I have contacted Epson, who tell me to try enabling "Load & unload device
drive" for all users in the Windows Security settings. Can anyone tell me
how to do this?