The Sound Manager prior to System Software 6.0.7 was known to have problems.
Our first suggestion is to install 6.0.7 on the Portable. The new Sound
Manager does have additional functionality. However, all previous interface
calls are still valid. The new Sound Manager has been totally rewritten,
providing a more robust tool.
Because the application appears to be working in certain environments, it would
seem one of the problems of the old Sound Manager becomes obvious when used on
the Portable. Using the new Sound Manager shipped with 6.0.7 should provide a
solution.