I am still seeing similar behavior that once it pukes with a "Track is too short" it goes to la-la land and doesn't try again. I loaded the new version and followed the instructions. I played a track off my harddrive and it submitted fine. Then I opened my lastfmproxy and launched a radio station. It puked as you see at 21:28. I let it roll for awhile then skipped that track and let the next track play for awhile. It did nothing until I closed XMP at 21:44.
2006-06-15 21:27:41 [DEBUG] DSP_SetFormat( 1, 0, 0 )
2006-06-15 21:27:41 [DEBUG] DSP_StopTrack
2006-06-15 21:27:41 [DEBUG] XMP_KillTimer
2006-06-15 21:27:41 [DEBUG] DSP_NewTrack (CLOSE)
2006-06-15 21:27:42 [DEBUG] DSP_Free()
2006-06-15 21:27:50 [DEBUG] DSP_New()
2006-06-15 21:28:14 [DEBUG] DSP_NewTrack (OPEN)
2006-06-15 21:28:14 [LIBSCROBBLER] ...
2006-06-15 21:28:14 [DEBUG] DSP_SetFormat( 1, 44100, 2 )
2006-06-15 21:28:14 [DEBUG] XMP_SetTimer( 0 )
2006-06-15 21:28:14 [INFO] Track is too short to be submitted (must be at least 30 seconds long)
2006-06-15 21:28:15 [LIBSCROBBLER] Handshaking: Client up to date.
2006-06-15 21:28:15 [LIBSCROBBLER] Submit interval set to 1 second(s).
2006-06-15 21:28:15 [LIBSCROBBLER] Handshake successful.
2006-06-15 21:44:00 [DEBUG] DSP_SetFormat( 1, 0, 0 )
2006-06-15 21:44:00 [DEBUG] DSP_StopTrack
2006-06-15 21:44:00 [DEBUG] XMP_KillTimer
2006-06-15 21:44:00 [DEBUG] DSP_NewTrack (CLOSE)
2006-06-15 21:44:01 [DEBUG] DSP_Free()
Thanks for your continued efforts. Your plug-in is still more reliable than last.fm's site