I think I've found a workaround for this problem. I say "workaround" because it basically involves changing a few things from their default settings, which doesn't really solve the problem so much as bypasses it.

Firstly, I found a series of options in the Group Policy Object Editor that deal with read/write permissions on hard drives and removable media. I basically changed their individual settings from "Not configured" to "Disabled". They are as follows:

Start > Run... > gpedit.msc > OK

Computer Configuration > Administrative Templates > System > Removable Storage Access [In here I disabled all of the "Deny read access/write access" options; you may only want to disable the ones relating directly to your type of media]

Do the same as above, except the first step is "User Configuration" instead of "Computer Configuration"

The second thing I did involves the registry. My post above regarding the Thumbscrew software already mentioned this, but I've since learned from browsing various forums that there's a little more to it.

Backup your registry before continuing. If you're not sure how, read on.

Start > Run... > regedit > OK

Highlight "Computer" and right-click. Select "Export" and save the backup somewhere safe. Just double-click it if you want to reset the changes you make.

Navigate to the following registry location:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\StorageDevicePolicies

Click on StorageDevicePolicies and on the right-hand side there should be a DWORD value labelled "WriteProtect". If there isn't one, create it. Either way, make sure it has a value of 0. Double-click it to change it.

Do the same with the following two locations (creating any non-existent keys/values along the way):

HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Control

I haven't had the problem since I did this, which was the same day as my last post (about a week) so I'm reasonably confident that this has put a stop to it. I hope so, anyway!

Thanks!