Just as a follow-up to this thread, I have been struggling with this problem ever since we upgraded all of our Panasonic Toughbook CF-31 computers to 64 bit. In most cases we are running Windows 7 Pro, but on some machines we are running Windows 7 Ultimate. On all of those machines the GpsGate Splitter will only work in the "visible" mode, and only when the user has administrator rights, if the Splitter is the free (2 Virtual Com Port) version. It does act as if it is working in the "Start as a Service" mode, but it does not send any data, and if a user logs on that does not have admin rights, it will not work in either the "visible" mode nor in the "run as a service" mode.
However we paid for the "pro" version of GpsSplitter, which is the exact same product but allows an unlimited number of virtual com ports to be created, and what I found was that once the paid version's license key has been entered, the Splitter will then run in the "Start as a Service" mode just fine, whether the user is logged in with or without admin rights.
So for now, it would appear that the "free" version is not compatible with Windows 7 Pro or Ultimate when running the 64 bit version, unless it is to be used in the "visible" mode, and with admin rights.