Go back to previous asset version

I updated my A* Pathfinding asset, and after it was done, none of my scripts would load. I get the error: "The associated script can not be loaded. Please fix any compile errors and assign a valid script." I also get an error about something in one of the asset's script, but that isn't so important. Besides that, I also get a couple of "SpeedTree materials need to be regenerated." I hvae no idea what SpeedTree is, or how to regenerate a material. Please help me, this has to work tomorrow.

Thank you for any help.