I am using a 3rd party library from Chilkat for FTP in an iPad application targeting iOS 5. I have installed the library by copying the sources into my project, modifying my Header Search Paths and adding -all_load to my Other Linker Flags. The 3rd party library provides header files and 2 files named libchilkatIos.a (in separate folders) - one for device and one for simulator. These files both now appear under the Build Phases - Link Binary With Libraries section. My application runs fine on the device but whenever I try to build or run it on the simulator it comes up with the following warning and error: ld: warning: ignoring file /Users/david/Development/Projects/DocsOnTap/Libraries/Chilkat-9.2.1-IOS-4.3/libDevice/libchilkatIos.a, missing required architecture i386 in file Undefined symbols for architecture i386: "_OBJC_CLASS_$_CkoFtp2", referenced from: objc-class-ref in DataLoader.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) I have other 3rd party libraries in my project which work fine on both device and simulator. I'm not sure what to do to allow me to run on the simulator? (I did try removing the libchilkatIos.a file that was related to the device, however that did not help). In the Chilkat installation instructions it seems to recommend having a different target for device and simulator, however I'm not sure how to do that - or whether that should be necessary.