Vista - Vista Home Premium 64bit loses itself?

I wanted to copy a large file, about 500MB from this machine to
another machine connected to my home network via a DLink router. The
transfer starts and about half way through I get a requestor telling
me that the connection to the file on the network server is lost,
which I assume is this machine, and to re-try or cancel. On the
re-try the same thing happens.

I thought maybe the file or this hard drive has a problem so I copied
it to another hard drive and tried again with the same result. I
worked around this by burning the file unto a CD and carrying it to
the other machine.

Anyone got any ideas what is happening here?

Al