FRITZ!Box 6660 Cable Service - Knowledge Base

FRITZ!Box 6660 Cable Service

Windows offline synchronization fails when using storage (NAS)

Windows offline synchronization fails when it attempts to save data to a USB storage device connected to the FRITZ!Box. The error message "The process cannot access the file because it is being used by another process" is displayed in the Windows Sync Center for each file it attempts to copy.


  • Windows offline synchronization can only reliably copy data to another Windows computer. Errors may occur when using it with network drives on computers with macOS or Linux and NAS (Network Attached Storage) systems such as the FRITZ!Box.

Issue is being examined

Our development department is currently examining the error. If an update for the FRITZ!Box can correct this behavior, we shall make a corresponding FRITZ!OS update available for the FRITZ!Box.

If you are leasing your FRITZ!Box from your cable provider, then your cable provider will make the FRITZ!OS update available, and not AVM. It will be installed automatically. In this case, refer to your cable provider for possible release dates for the update.