Since you are using GSS 2.5, have you tried using Winpe as your preos that is being used as default for all clients? Since you dont mention where your problem actually happens I presume you are saying "when I execute task and client machine goes to DOS preos and then cannot contact server".
If you are getting 'drivers cannot be found' then perhaps you were trying to execute task under Winpe preos? If it tells you that drivers cannot be found for Winpe and you have tried drivers that comes with GSS, then go to manufacturing website, select your driver for Vista, download it and import it to GSS driver database using Ghost boot wizard (Select Winpe->Edit->Eidt). Once imported, add it to Winpe of your choice and compile it. It will finish in a few minutes and your Winpe is ready to be used.
Cheers.