Terminal: What does intermittent "cp: .: Invalid argument" mean? Very often I get an error message on the terminal "cp: .: Invalid argument". It also happens with other commands than "cp". For example:

me@iMac:/Volumes/boot$ cp ~/Documents/wpa_supplicant.conf .
cp: .: Invalid argument
me@iMac:/Volumes/boot$ cp ~/Documents/wpa_supplicant.conf .
me@iMac:/Volumes/boot$


Note that I did not re-type the command on line three, I just hit up-arrow and enter. Does anyone know what the problem could be, or have an idea how to debug?

Thanks, Martin
Set your hard disks to never sleep in System Preferences and see if the issue still persists.