Difference between ''おつかれさまでした'' and ''ごくろさまでした'' ??

Question

Answer

you can say ごくろうさまでした to someone younger than you or someone works for you (目下の人).  it is not appropriate to say to older or your boss  (目上の人).

please check out this page.
http://manner.fideli.com/manners/m/detail/ei/1/index.html

Answer

お疲れ様でした(おつかれさまでした)
 could be used as a daily greeting.

ご苦労様でした(ごくろうさまでした)
 could be more used as a greeting on appreciation for a specific action that someone made for you.