failure to determine file ownership

I am running Vista Ultimate on a Packard Bell Easy Note with 2 Gb memory and
dual core processor.
I have a problem with a file I copied to my desktop.
It was a video file created with my mobile phone and was amongst a lot of
files on the storage card which I made a copy of whilst installing a bigger
SD card in my phone.
I was able to copy from the original sd card to the desktop and then from
the desktop to the new bigger sd card without problem but when I tried to
delete the copy on my desktop it kept telling me I did not have permission.
I eliminated all the files and folders one by one until there was only the
one video file left.
When I looked into the security on the file vista said it could not
determine ownership of the file and would not let me assume ownership.
I tried all the usual tricks of running windows explorer as an administrator
and tried to assume ownership of the file as instructed in the help section
buit would not let me do anything with it.
I cannot move it or rename it nor can I move or rename the folder structure
it is in.
Does anyone have any ideas on how to delete such a file?
I now have a folder on my desk top with sub folders all of which are empty
except for this one file several folder layers down and I can't do anything
with it.
Pease help if you can otherwise it is going to drive me round the bend.