Hi fellow Pro Tools users,
We're currently working with the Digidesign developers to solve the compatibility issue between our soft synthesizers and the Pro Tools platform, especially under the Mac OS X Leopard system.
In order you to go on using the Arturia synths in your projects, here is a workaround that should help.
Go to the menu:
Setup > Playback Engine
RTAS Processors: 1 Processor
Possibly, you may consequently adjust the H/W Buffer Size and/or CPU Usage Limit settings.