Yep - seeing exactly the same thing as the poster. Using XCode 4.0 (Build 4A119a), and the latest from CorePlot.....
It also tells you to import QuartzCore (which I did, and I assume the poster did as well, cos it's still broken :-)
The CorePlot docs say that you can put the SDK anywhere you like, and mentions both ~/Library and /Library as appropriate places. I tried both and got the same error (although the error appeared more quickly when it was in /Library, but this could be unrelated).
It fails this way whether the target is the iphone, or the simulator (I checked that because the CorePlot sdk is different for the two).
One thing that I noticed is that the plist entries for the two sdks indicate that they are for iphoneOS 3.0 rather than 4. That might be worth checking.....
Cheers
Peter
p.s. wondering if it might be a resurfacing of this issue: http://www.mailinglistarchive.com/[email protected]/msg17993.html
I'll fiddle around and post back if I can get it working....
Update: I gave up on XCode 4 as it kept crashing and is still way too buggy for primetime. Back on XCode 3.2 it all compiled and ran fine.... I think I'll wait until a new version of XCode comes out before trying it again.