ignoring file [path] missing required architecture i386 in file
This warning means that you're trying to use library made for Device (ARM) with your Simulator (i386).
You can use this terminal command to create a universal library:
lipo -create lib_arm.a lib_i386.a -output lib_universal.aMore info about lipo command here.
Change your target's "Build Settings > Build Active Architectures Only" to "No"
This is doing the same thing as Dmitry Zhukov's answer but doing it thru Xcode instead of going around its back.
If you are working with a 3rd party code, keep in mind that some SDKs may not work on the simulator. The same build error I have encountered vanished, when I ran the project on the device.