Error 0 on a GT tuner means that a file that the GT is looking for cannot be found. The filename it cannot find is listed on the error screen.
The first thing to try is to update the GT tuner with the latest update using the Update Agent. This should load the needed files.
In some instances, particularly on older software, and other times it may be necessary to call our tech support with the tuner and a Windows PC to manually load the needed file(s). If this is the case, please either take a picture of the error code screen or note down everything on the screen. The Agent will need this information and this will speed up the process with the Tech Support agent.