Drum contraption "Invalid parameter passed to (null), (null), (null) line 0

I get this message when altering values in a drum contraption when the contraption changes patch in automation playback. The error message compounds so as I mouse to OK the original error, new ones pop up making the error fairly unrecoverable.

I'm running WinXP on VirtualBox 3.04 on Ubuntu Jaunty (9.04). I guess the environment *might* be a contributing factor with this bug, but it is otherwise stable.

Cheers

Stuart