Comment 4 for bug 892333

"Resource not found" means either gstreamer can't open the file, or it can't open the audio output.
As you can play the file on a second try, It means it is the latter.

It may be caused by the audio driver not allowing multiple connections, and somehow the connection from the previous file was not yet closed when opening the connection for the next file.

You can try changing the output device in the audio tab, to pulseaudio or alsa.
You can also try enabling the gapless option in the advanced options for gstreamer, also in the audio tab.