Network while display sleep

Hi to all,
I have Backblaze do backup my mac to the cloud. Since I have a huge amount of data to backup I've been leaving the computer tuned on all the time to backup.

I've went to the Energy Saving Preferences and unchecked everything. Still
I verify with the Lion the following:

- If I leave the computer with a certain time to the display to sleep after like 20h when I come back, I click one button to wake the display up and I realized he didn't backed up almost anything.

- If I leave the computer without the display sleep and manually just lower the brightness of the display to a minimum he backups for the whole period.

Seems like, when the display sleeps, somehow he just disconnects from the network....

Is anybody experiencing something like this?