iPhone CorePlot - Strange error

I downloaded the CorePlotSDK, installed it using 开发者_如何学JAVAthe readme instructions: copied the coreplotsdk directory to ~/Library/SDKs/ - imported in the PCH file - added $HOME/Library/SDKs/CorePlotSDK/${PLATFORM_NAME}.sdk to the additional SDKs and -ObjC -all_load -lCorePlot to the other linker flags setting.

Now, if I try to build the project, I get this error:

Internal error occurred while creating dependency graph: *** -[NSCFDictionary setObject:forKey:]: attempt to insert nil value (key: SDKRootPath)

What's that?!? I've never seen it and google can't help.