A few questions need answering...
What memory card?
How are you importing? Via card by taking card out or straight from the camera?
What frame rate and size? i.e. 60f 720hd
Also, spec of PC or Mac and how old... What software are you using for playback...???
I'm not very tech savvy, so I will answer this the best that I can.
It's a GP Hero 3, not the plus. From what I can tell, the mem card says "PNY " with a 4 on it. I'm importing by plugging the camera in and dragging the files over. I've never had a problem with this method before with the other footage I've taken. I have no idea of the frame rate and size.
From the brief Googling I did, it seems like this is a common-ish issue with the cameras. I did a hard reset and it seems to have solved the issue, for now. I'm just super nervous this is going to happen again.
Deagol, I was reading that as well about constantly needing to update the firmware and micro SD card.
I'm just frustrated right now since I lost A LOT of footage from my trip, and it's not something I will ever get back.