Xcode error while compiling: ld: symbol(s) not found for architecture x86_64 clang

Question

I'm developing an iOS application which no had problems when compiling the project. But now, when I try compile I get the following error message:

Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_CKCalendarView", referenced from:
      objc-class-ref in CITSearchCarViewController.o
      objc-class-ref in CITAddNewDestViewController.o
      objc-class-ref in CITSearchViewController.o
      objc-class-ref in CITNewFlightAlertViewController.o
  "_OBJC_CLASS_$_HMSegmentedControl", referenced from:
      _OBJC_CLASS_$_CITSegmentedControl in CITSegmentedControl.o
  "_OBJC_CLASS_$_IBCoreDataStore", referenced from:
      objc-class-ref in CITSearchHistory.o
      objc-class-ref in CITJourneyData.o
      objc-class-ref in CITAlertManager.o
  "_OBJC_CLASS_$_MKNetworkEngine", referenced from:
      _OBJC_CLASS_$_CITNetworkEngine in CITNetworkEngine.o
  "_OBJC_CLASS_$_SSZipArchive", referenced from:
      objc-class-ref in CITUtils.o
  "_OBJC_CLASS_$_SVProgressHUD", referenced from:
      objc-class-ref in CITInitialViewController.o
      objc-class-ref in CITFlightAlertViewController.o
      objc-class-ref in CITSearchViewController.o
      objc-class-ref in CITSearchResultsViewController.o
      objc-class-ref in CITMultiDestViewController.o
      objc-class-ref in CITConfigurationViewController.o
      objc-class-ref in CITFlightDetailViewController.o
      ...
  "_OBJC_CLASS_$_TRAutocompleteView", referenced from:
      objc-class-ref in CITAddNewDestViewController.o
      objc-class-ref in CITSearchViewController.o
      objc-class-ref in CITNewFlightAlertViewController.o
  "_OBJC_METACLASS_$_HMSegmentedControl", referenced from:
      _OBJC_METACLASS_$_CITSegmentedControl in CITSegmentedControl.o
  "_OBJC_METACLASS_$_MKNetworkEngine", referenced from:
      _OBJC_METACLASS_$_CITNetworkEngine in CITNetworkEngine.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I've tried to change the architecture i386 to x86_64, but I get the same result. Initially the problem was caused because Xcode not found the lpods library. Then I tried to "clean & build" to the project but this either works.

What can I do?