[RESOLVED]: I did not set up the correct settings for all of my build targets, and that is why I was getting an error. The "red text" is apparently caused by a bug in Xcode 4, as that does not go away when I build successfully. I am getting the error below when I try to build. I am building an iOS app. Any idea why this would be happening? Code: Undefined symbols for architecture i386: "_OBJC_CLASS_$_SDWebImageManager", referenced from: objc-class-ref in ViewController.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) I am using Olivier Poitrey's SDWebImage static library: https://github.com/rs/SDWebImage Here are my build phases: Note: The problem might be with the red text, meaning that the compiler cannot locate the .a file. Supposedly, this is the file that is produced when the library is built. However, I can not seem to find it anywhere when I build the SDWebImage library separately.