We are running Presentation Server 4 on Windows 2000 SP4 and we have one application (an EKG app called MUSE from GE) that produces a GPF when run from the console, ICA, or RDP. If PS4 is removed the app works fine with RDP and local at the console. I called Citrix Tech Support and the only help they could provide was a workaround. If I remove mfaphook from the registry and not allow it to load then everything is fine. MUSE is an app with 16 bit drivers and runs in its own ntvdm...Anyone have any other ideas and if not what is the drawback of not loading mfaphook? I asked Citrix Support that question and he said he needed 48 hours to research it.. Thanks!