Backup stops with WriteFileNoCache

Config:
2 Vista laptops doing weekly incremental backups weekly
ATI 2011
Backup over WiFi
Backup Target is NAS connected to WiFi router

Problem:
I've had this problem since ATI 2009, and have never been able to fix it... I've replaced the NAS and also the WiFi Router in hopes of getting a smooth running backup. This happens on both laptops.

Typically the backup runs for awhile, and eventually stops with an error. I click retry and it proceeds as if nothing had happened. I've tried all settings I can think of, throttling the disk i/o, network i/o, compression settings, and nothing I do has fixed this. I read a few other messages with similar errors and there does not seem to be a solution. There are no errors, no outages, no problem detected except for the failed backup.

Log shows (today, it failed twice..)
1 Information 2/18/2011 9:00:02 AM Operation FUJITSU MHZ2250BH G2 started.
2 Information 2/18/2011 9:00:02 AM Analyzing partition '0-0'...
3 Information 2/18/2011 9:00:03 AM Analyzing partition '1-1'...
4 Information 2/18/2011 9:00:03 AM Analyzing partition 'C:'...
5 Information 2/18/2011 9:00:04 AM Priority changed to Low.
6 Information 2/18/2011 9:00:24 AM Create Incremental Backup Archive From: Disk 1 To file: "" Compression: Maximum
7 Information 2/18/2011 9:00:28 AM Pending operation 147 started: 'Creating partition image'.
8 Information 2/18/2011 9:00:28 AM Locking partition 1-1...
9 Information 2/18/2011 9:00:28 AM Pending operation 147 started: 'Creating partition image'.
10 Information 2/18/2011 9:00:28 AM Locking partition C:...
11 Error 2/18/2011 9:28:03 AM Error occurred while writing the file.
function="WriteFileNoCache"
13 Information 2/18/2011 9:28:03 AM Error occurred while writing the file.

Click Browse to specify another location, Retry to try again, or click Cancel.: ⎂Retry//⎂Cancel/
14 Information 2/18/2011 9:28:20 AM Error occurred while writing the file.

Click Browse to specify another location, Retry to try again, or click Cancel.: ⎂Retry//⎂Cancel/: User response: ⎂Retry
15 Error 2/18/2011 9:37:20 AM Error occurred while writing the file.
function="WriteFileNoCache"
17 Information 2/18/2011 9:37:20 AM Error occurred while writing the file.

Click Browse to specify another location, Retry to try again, or click Cancel.: ⎂Retry//⎂Cancel/
18 Information 2/18/2011 9:37:50 AM Error occurred while writing the file.

Click Browse to specify another location, Retry to try again, or click Cancel.: ⎂Retry//⎂Cancel/: User response: ⎂Retry
19 Information 2/18/2011 9:42:44 AM Pending operation 144 started: 'Saving partition structure'.
20 Information 2/18/2011 9:42:45 AM Operation has succeeded.