With the release of BS3, Brad instituted a user requested feature to limit the ABV to the maximum published value for the yeast strain being used. The change is documented in the initial release notes for BeerSmith 3 on Brad's blog. You can unblock this by editing the yeast entry and changing the maximum ABV tolerance for the yeast. It does mean that it is wise to double check the yeast manufacturer specifications versus what is presently in BeerSmith, as most of the yeast providers update the specifications on a regular basis.