This will almost certainly be to do with the revised security and permissions controls used in XP.
Whilst your logged in user can access the DLL program your batch process does not have the same permissions and so the program is unavailable to it. Hence the message.
I would imagine that the IT people responsible for your desktop setup should be able to rectify that problem without breaching any security policies they have defined. I cannot claim expertise in that area as I don't need to run with secure parameters.
Hope this helps in some way.