import "cocos2d.h" works in some files, but not all
Turns out I had only added the "user header search paths" to my target, but not in the project settings.
Adding it fixed the problem. I guess the reason it compiled fine was because I had added it to the target, but it didn't work in the text editor since I hadn't added it to the project.
This happened to me as well, even though I did add it to both project and target.
However, what worked for me was to select the RECURSIVE checkbox under "User Header Search Prefixes" (which was set to "/lib/**")
I had same issue.
My project -> Build Settings
Look for the entry for Search Paths
Always Search User Paths - YES
User Header Search paths - "myProjectName/libs" //I put box2d folder here
Hope this help someone.