file was built for archive which is not the architecture being linked (i386)

Your libnetUtils.a is being built for a different architecture than your target.

Check the libnetUtils build settings. The architectures that it is being built for and its list of supported architectures must be a (weak) superset of your target's architecture. The complexity here is that the resulting architecture is spread over various settings: "Architectures", "Build active architecture only" and "Valid Architectures".

"Build active architecture only" settings make this particularly confusing. For example, suppose you are building for the simulator. If the "Build active architecture only" setting for Debug is set to NO, it will be building all the architectures listed in "Architectures" and "Valid architectures" (probably armv7, etc). But if libnetUtils has that setting set to Yes (Debug: Yes) it is only building for i386. So when your linker tries to link armv7 with i386, it fails.

If I get the ignore file warning - I would run lipo -info on ignored file to find it's architecture as below

lipo -info libnetUtils.a

That would print either of i386, armv6, armv7, armv7s, x86_64 etc. In general, that architecture has to match with your target build platform. E.g.

• i386 = ios simulator or 32 bit build on mac os x
• armv6 armv7 arm7s = ios device
• x86_64 = 64 bit build on mac os x

Depending on the mismatch, either you have to rebuild your library for your target platform or change your target platform.

Note: For fat binaries, lipo -info will print a combination of above architectures.

Sometimes these types of errors irritates you!

Removing Derived Data Works for me:

Steps to fix

1) In XCODE > Windows > Project > Select your project > Delete derived Data > Quit XCODE and Reopen it > If you get MAC-O-Linker builed failed error > Refere this link > Clean and Build again.

After struggling with this same problem and following all the accepted answers of updating build settings, clearing the linker search path, etc.. I finally discovered an answer that worked for me.

Before building, make sure you select right type (iPhone Simulator) instead of iOS Device. Then rebuild. Otherwise, you're trying to use a library built for an iOS device (arm processor) on a simulator on your mac (i386). Should've been obvious, but wasn't.

Before:

After:

Now, look in the Products group in the Navigator > right click your static library (.a file) > Show in Finder, you'll notice that its in a Debug-iphonesimulator folder instead of Debug-iphoneos. I didn't pay any attention to the folder name originally, or I might have thought of this sooner.

Hope this helps.