I have a project that has one target dependency. The target dependency is dependent on a framework called Three20.
The dependency tree looks like this.
Had the same problem in a case where I got a workspace working, closed it, copied the containing folder to a USB drive, then reopened. I got that message for one of the projects in the workspace. Closed, tried again, removed/re-added project - no luck. Closed, tried to open the project alone and got the message about it being open in another workspace - not true. Quit XCode, restarted by double-clicking my workspace in Finder, and all went well after.
I had the exact same problem. Quitting the xcode completely and opening it up again worked.
I have close the Xcode completely but IT didn't work. I have killed the procces and It did finally!!! :-)
Quitting Xcode alone didn't work for me. What I did was:
I had same problem. Fixed after updating of cocoa pods with pod update command.
Restart the computer and try again opening the project :)