Damn ye, Adobe. There be bugs in that 1.4 update that you rolled out.
For other folks who use a pc and like to convert to .dng while importing, this update is no good.
I too am getting the "an unknown error has occured" when trying to view my files at 1:1 size. Solution (so far) has been to downgrade to the 1.3.1 release, available here:
Win: http://www.adobe.com/support/downloa…jsp?ftpID=3815
Mac: http://www.adobe.com/support/downloa…jsp?ftpID=3810
Also see this post detailing the problems, courtesy of the Lightroom Journal: http://blogs.adobe.com/lightroomjournal/2008/03/important_lightroom_14_and_cam.html
That’s what you get for being such a bleeding-edge nutcase