Vista - Cannot paste files over network

I have a main computer, Vista Business, and a Vista Home Premium computer which I use to back up my files to every few days. They are connected via Ethernet cables to a router. The network worked fine until a couple of days ago when I moved my Home computer after disconnecting the Ethernet cable and reconnecting it while the computer was switched off. (This should make no difference at all!)

Now when I try to paste files which have been backed up on my Vista computer to the F:\ drive on my Home computer I get the message 'Y:\ refers to a location which is unavailable. It could be on a hard drive on this computer, or on a network. Check to make sure that the disk is properly inserted, or that you are conneted to the Internet or your network, and then try again. If it still cannot be located, the information might have been moved to a different location.'

What is strange is that I can see the directory structure and paste files to anywhere on my Home computer's F:\ drive, except files which are created by the Business computer's backup program.

Has anyone any idea what the problem is please. I have not changed the permissions on either computer for a long time, but is it something to do with permissions?

Viv

I forgot to add that I can paste the files to the directory I want if I save them to a memory stick and then paste them from there to the Home computer, but the same files cannot be pasted via the network, as I have done for months.

Viv