subsonic in VirtualBox stops playing after 1 sec. in jukebox

[tuhl]

Problem Description:
subsonic stops playing (in a VirtualBox) after the first second having sound on the host side (jukebox mode).

Troubleshooting Steps:

first of all, Subsonic works well, if it is placed on the same host where the sound card exists.

I use the Jukebox mode.
Now I moved subsonic to a Virtual Machine (VirtualBox) with no virtual sound card (having deactivated because of conflicts between host and guest system)
I placed the variable PULSE_SERVER system wide to /etc/environment and checked in /etc/init.d/subsonic with an echo $PULSE_SERVER.
The pulseaudio server is daemonized on the host system and enabled to receive TCP packets.
Other sound applications like aplay, mplayer etc can play music on the remote (host) system - from the virtual machine - without any problems.
On my virtual subsonic server, If I select a song to play, I can hear the first second, the the sound stops and the error appears in the log.
If I test again with the subsonic on my host (Version 4.2 (build 1944) – 21. November 2010, Server jetty-6.1.x, java 1.6.0_18, Linux (245,9 MB / 455,2 MB))
sound is available from the same song via pulseaudio.

the subsonic.log shows
WARN JukeboxService - Error in BasicPlayer.play()

Playback Application and version:
From a Firefox 6.02 on a Ubuntu 11.04 32 bit workstation (generic-pae kernel) to a
Ubuntu 11.04 32 bit in a headless VirtualBox guest system,
hosted on a Ubuntu 8.04 (hardy) 64 bit System, running pulseaudio server (daemon)

Subsonic Version:
Version 4.5 (build 2384) – 10. August 2011

Server Version:
Server jetty-6.1.x, java 1.6.0_22, Linux (175,4 MB / 237,8 MB)

Last log file lines:
tail -f /var/subsonic/subsonic.log
at net.sourceforge.subsonic.service.NetworkService$Task.run(NetworkService.java:309)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRunAndReset(FutureTask.java:351)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:178)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:165)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)

[2011-09-17 21:57:34,772] INFO SubsonicLdapBindAuthenticator - User 'thomas' successfully authenticated in LDAP. DN: uid=thomas,ou=People,dc=tuhlix,dc=local
[2011-09-17 21:57:35,112] INFO VersionService - Resolved local Subsonic version to: 4.5
[2011-09-17 21:57:35,447] INFO VersionService - Resolved latest Subsonic final version to: 4.5
[2011-09-17 21:57:35,448] INFO VersionService - Resolved latest Subsonic beta version to: 4.5.beta2
[2011-09-17 21:57:48,827] INFO JukeboxService - Starting jukebox player on behalf of thomas
[2011-09-17 21:57:48,846] DEBUG JukeboxService - stateUpdated : OPENING:-1:java.io.BufferedInputStream@266b44
[2011-09-17 21:57:48,864] INFO PlaylistInputStream - thomas listening to "Van Morrison - Astral Weeks/01 - Astral Weeks.mp3"
[2011-09-17 21:57:48,953] DEBUG JukeboxService - opened : {mp3.id3tag.track=01, mp3.crc=true, mp3.copyright=false, album=Van Morrison - Astral Weeks, mp3.version.mpeg=1, mp3.channels=2, author=Van Morrison, mp3.framesize.bytes=623, title=01 - Astral Weeks, mp3.version.layer=3, mp3.bitrate.nominal.bps=192000, mp3.vbr.scale=0, mp3.version.encoding=MPEG1L3, audio.type=MP3, mp3.id3tag.v2=java.io.ByteArrayInputStream@9c2192, vbr=false, mp3.id3tag.v2.version=3, mp3.padding=true, audio.framerate.fps=38.28125, audio.channels=2, mp3.framerate.fps=38.28125, mp3.frequency.hz=44100, mp3.header.pos=1567, basicplayer.sourcedataline=org.classpath.icedtea.pulseaudio.PulseAudioSourceDataLine@1b5d2b2, bitrate=192000, mp3.mode=0, mp3.vbr=false, audio.samplerate.hz=44100.0, mp3.original=true}
[2011-09-17 21:57:48,957] DEBUG JukeboxService - stateUpdated : OPENED:-1
[2011-09-17 21:57:49,003] WARN JukeboxService - Error in BasicPlayer.play()
[2011-09-17 21:57:49,007] DEBUG JukeboxService - stateUpdated : PLAYING:-1

-thx
-thomas