Hi...not sure if I am in the right forum....new to Logic 9...does anyone know how to prevent undo history from being deleted when closing Logic?

Hi LP, Yes, this is the correct forum :) I'm afraid I believe it is not possible... this was one of the changes from Logic 8 to 9... not sure why, I'm sure the developers had their reasons, but the result is that undo history is purged when you close your project. I'd recommend saving backup versions of the project at critical editing... you'll find these in the project backups folder.