Did your library contain any categories?
If so, I think you should follow these steps to get it work:
- In Xcode, double-click the target's name under "Targets" in the Project window.
- Choose the Build Settings panel.
- Scroll down to the "Other Linker Flags" build setting under the Linking collection and set its value to "-all_load -ObjC".
Please refer to corresponding Apple Documentation
Here is a related question: Objective-C categories in static library