Vista - Transfer files between two external drives?

Hi,
I have two USB harddrives and I want to transfer some files from one to
the other.
Attempting to do so makes Vista inform me that I need permission to do
that.
And that's it. No "click here to give permission", no "enter a
password", no nothing.

How do I get this mysterious permission, so that I don't have to spend
five hours transferring files across in batches?

My mistake...
There appears to be some level of file management going on on the
target drive.
The folder I was attempting to paste to had somehow been designated a
system folder, or similar.
Started moving stuff to a different folder, and it works fine.

Strangely, I'd had the same problem with two non-managed USB
thumb-drives last week. That was a different (Still unidentified)
problem, but much less important than this mess.

Cheers, anyway.