[pluggo] problem rendering a pluggo vst plugin in Wavelab

Hello,

i've made a pretty simple patch to decode/encode
an incoming M/S stereo signal (plugin) and send the result
to the output (plugout). I've made it into an VST plugin.

I can use it in Wavelab as a vst plugin and it works perfect.
Now if I want to render a file in Wavelab using this plugin,
all i get is silence. what could I be doing wrong?
  

apps:
Windows XP sp2
Wavelab 5
pluggo 3.5
max-msp 4.5
on an Intel Pentium D 3.0 GHz