Some Panasonic AVC-LongG clips are not supported in Motion, Compressor, QuickTime Player 7, and other QuickTime based applications. Specifically, AVC-LongG12/6 8-bit 4:2:0 media is supported but AVC-LongG50/25 10-bit 4:2:2 media is not. All AVC-LongG (50/25/12/6) media are supported in Final Cut Pro X 10.1.4 and later.
If you want to be able to use AVC-LongG media in Motion, Compressor, QuickTime Player 7, and other QuickTime-based applications, use Final Cut Pro X 10.1.4 to export to ProRes 422 or ProRes 422 HQ, then import the ProRes clips into Motion or Compressor, or QuickTime.