I have this working for me now, but I am not sure what the exact fix was. I was seeing a bad OU name and invalid static route being applied in the modify config task.
In my opinion, this is related to bugs with Windows 7/2008/Vista when Altiris is doing commands to backup/restore IP configuration settings. (By the way, I wish there was more visibility on the commands being run by Altiris).
To fix this you should...
1. Make sure all of the IP and DNS settings are good on the target machine before you do anything else!
2. If you have an Altiris job that does the modify configuration, clear all the job history by deleting the failed operations from the Altiris console. Then ensure your jobs only apply good settings. I have made sure we specify only domain-specific settings in the modify config job, and made sure we DON'T specify anything that is 'generic' to the environment, such as default gateway. This seems to work.
3. On your target machines and master images, remove all invalid entries from these reg keys:
HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\PersistentRoutes
HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\DNSRegisteredAdapters
Also make sure you have valid settings for these registry values:
HKLM\System\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<GUID>\
DefaultGateway = <default gateway IP>
DefaultGatewayMetric = 1
4. Recommend obtaining and installing these hotfixes:
http://support.microsoft.com/kb/979101/
This is for another bug with 'netsh' command in Vista etc, but it may not be giving you any problems. The hotfixes didn't make any difference to the config failure.
5. Ensure you are on Altiris DS6.9 SP4 with agents version 453.
6. If you have worked through all of the above settings you should find that your modify config task will work properly on Win 2008 etc.
This is what worked for me. Hope it helps someone.
Mike R.