I don't have GSS available here, but does the execute dialog have a separate field for command line parameters?
Second question. If the account that is trying to execute a file on T: is a system account, it is not going to have network access, and I'm going to assume that the T: drive is not a local hard disk. As a test, copy the bat file to a local hard disk and amend your command line to run the bat file from there. If it works then you will know it's an access issue.