I'm seeing this quite often, too on this machine:
MacPro (early 2008) 2x2,8GHz Quad-Core, 16GB RAM; NVIDIA GTX 680, USB 3.0 G-Drive, Mojo DX
OSX 10.11.4 / Media Composer 8.5.3
The playback stops and when I click OK, I can continue.
I'm seeing this quite often, too on this machine:
MacPro (early 2008) 2x2,8GHz Quad-Core, 16GB RAM; NVIDIA GTX 680, USB 3.0 G-Drive, Mojo DX
OSX 10.11.4 / Media Composer 8.5.3
The playback stops and when I click OK, I can continue.