Hi,
I'm not seeing this crash on my Mac (Lion) build 48 and I have tried several test cases (new recipe, old recipe, etc...) all clicking the mash tab.
Can you provide any other details such as the error message you receive?
Any old data should be in your backup files (Documents/BeerSmith/Recipe1.bsmx, Recipe2.bsmx, etc...)
If I could get it to occur here it would be very simple to correct it.
Brad