Mail.app won't launch Skim in Mountain Lion I have been using Skim for a while as my standard PDF reader. After migrating to a new MacBook Air with Mountain Lion (currently running 10.8.2), I can no longer launch Skim from Mail.app.

This same issue was reported to the Skim community ( http://sourceforge.net/tracker/?func=detail&amp;aid=3557462&amp;group_id=192583&amp;atid=941981 ) and closed as invalid, as it was considered a problem with Mail.app, not Skim.

Does anyone know how to get this to work again?
I experience the same problem. I upgraded to OS X mountain Lion and I can confirm that opening .pdf attachments with skim fails when done directly from Mail. 

The only workaround I know is to first save the .pdf somewhere (for instance the Desktop folder) and then skim works normally again.