The most likely cause is that you are using old structures or modules which aren't supported with the KDE 2 version. Unfortunately the documentation which is on the web refers to aRts-0.3.4.1 which is quite outdated. The most often reported crash is: that performing an execute structure in artsbuilder results in the error message [artsd] Synth_PLAY: audio subsystem is already used.
You should use a Synth_AMAN_PLAY instead of a Synth_PLAY module and the problem will go away. Also see the artsbuilder help file (hit F1 in artsbuilder).
Recent versions of artsbuilder (KDE 2.1 beta 1 and later) come with a set of examples which you can use.