cruzer 4G usb drive. Trouble adding files

o/s- windows xp

Just bought flash drive. Can sometimes add pics, mp3’s etc. But every time I go to add a film approx 500mb. It starts the process then fails. “cannot copyxxxx. Cannot find specified file”. When I then open my computer and click on flash drive. There is no files from the drive itself or that that were previously added. I remove flash, reinstall. Click to open and I can then see files that were added. And the icon of failed film copy.

 The drive works ok on net book with music pics etc. But I have no film files on there to test if same thing happens!! I also occasionally get the dmbackupdill error come up from time to time.

Please, any ideas.