iOS - file does not contain an armv7s slice
Try setting the Build Active Architecture Only to 'YES' in the Project Build settings.
libAddThis.a needs to be built for the armv7s architecture. If you don't have control over this then you will need to remove armv7s from valid architectures as you did.
I did this by changing valid architecture from build setting. I am attaching a screenshot for your help.
Thanks,Cp