Backup Nas to USB

Hi,
i have windows server 2008 I installed Acronis backup and recovery 10 update 3, I use it to backup the internal disks of an external USB and all is well.
I need to use it to backup a NAS to a USB external drive connected to the server, this tack always closes with the error after 5 seconds. The task is configured to get files from a mapped drive and put them on a usb disk, can make the calculation of the space properly. This is the error that gives me back ... can not seem to access the NAS

Code: 262161 (0x40011)
An unknown error occurred during backup.
Nothing to be archived.

Error Code: 0x40011
Tags: 0xBA19E88DC5FEA021

Thanks in advance to all