A .OPL file is an OpenPilot log file, LibrePilot also uses .OPL for that.
The GCS version must match the firmware in the CC3D. If it is still under warranty, you may want to find a matching OpenPilot install (15.02.02 maybe). Then you won't have to configure and tune it before flying it, there is a bit of a learning curve to that.
Sometimes a really old bootloader version is an issue too.