More information is needed.
Where are you copying the file(s) from?
From the computer/mobile device to the My Cloud or the My Cloud to the computer/mobile device?
What computer operating system/mobile device system are you using?
What software program or mobile app are you using to copy the file?
If using a Mac see the other thread where people are having trouble recently (very possibly due to a recent OS X update) copying files between a WD My Cloud a OS X/iOS device.
