The generated Xcode project does not have double quotes around Header Search Paths. Getting rid of spaces in your directory structure will fix this but you can also fix it by adding double quotes around the entry in Header search paths.
The QCARUnityPlayer.h is in unityproject folder projectname->Assets->Plugins->IOS,
copy this data to the XCode projectfolder projectname->Classes. Than its ok, I have this prob after the Unity Update to 3.5
The QCARUnityplayer.h is in Unity project folder Projectname->Assets->Plugins->IOS copy to the Xcode Folder Projectname->Classes. After the update to Unity 3.5, i have this prob.