Debugging Undefined symbols for architecture x86_64:

After some googling my conclusion is that there is more than one cause for this error.
Trying to add a scheduling library, ofxlCalendar to my project.

It was compiling fine, now for some reason, I keep getting the above errors.
Tried one suggestion, changing my architecture to Universal in Xcode, no difference.

If I comment out the following lines in my setup, everything compiles fine. Panic time as a deadline for launch approaches. Any feedback appreciated!

//SCHEDULE
 // update it every hour
 calendar = ofx::Time::ICalendar::makeShared("foo.com.ics", 600000);

calendar->reload();
calendar->startThread();

watcher = ofx::Time::ICalendarWatcher::makeShared(calendar);

watcher->registerAllEvents(this); // register this class for all events