Are you using the latest version of TurboActivate (3.2.2)? If not, update to the latest version and try again. And if you're using TA 2.x, then you can't just replace the libTurboActivate.dylib file. That will mess things up. You actually have to recompile your app and use the latest header/integration file (e.g. TurboActivate.cs for C#, etc.).
Does that make sense?
If you're already using the latest TA in your app, then make sure the Timezone is correct as well. Then have them restart their computer.