You should be logged on as Administrator unless you require a reduced rights account. The key here is that you need to disable User Account Control and leave it disabled. For Vista users, it would also benefit you to create your data file under the /My Documents folder structure such as create a folder /My Documents/My Logbook Data and that's where your .LBK file can be stored. With UAC disabled it really doesn't matter, but for those that end up with UAC turned back on for some reason and you're trying to work with a data file in C:\Program Files it is going to trigger UAC.
Logbook Pro works great on Vista, I've been using Vista since Nov '06, we have many users running Windows Vista. I suggest after disabling UAC to reinstall Logbook Pro. If you require any further assistance, feel free to submit a support ticket. Windows Vista is FULLY supported.