The mistranslation of harpagmos in Philp 2:6 as "robbery" is unfortunate. The translation as "grasped" is also incorrect. The preface of the NIV explains the long search for the correct meaning. The correct meaning was not learned until 1972 following the establishing of the Thesaurus Linguae Graecae in Irvine Ca. which aided scholars in correctly translating many obscure words.
ETA:
The Committee on Bible Translation worked at updating the New International Version of the Bible to be published in 2011
In it's notes under "Progress in Scholarship" it discusses the following change:
When the NIV was first translated, the meaning of the rare Greek word αρπαγμον /harpagmos, rendered ‟something to be grasped,” in Philippians 2:6 was uncertain. But further study has shown that the word refers to something that a person has in their possession but chooses not to use to their own advantage. The updated NIV reflects this new information, making clear that Jesus really was equal with God when he determined to become a human for our sake: ‟[Christ Jesus], being in very nature God, did not consider equality with God something to be used to his own advantage.”
A short excerpt from the 25 page Harvard theological review article αρπαγμον /harpagmos, by Roy Hoover, referenced in the NIV.
‘O petros de arpagmon ton dia stavrou thanton epoieito dia tas soterious elpidas”
(And Peter considered death by means of the cross harpagmon on account of the hope of salvation, Comm in Luc 6)
“Tines…ton thanaton arpagma themenoi ten ton dussebon moxtherias”
(Since some regarded death as harpagma in comparison with the depravity of ungodly men. Hist. Eccl VCIII,12.2)
Not only are arpagma and arpagmos used synonymously in these two statements, but they are used synonymously by the same author in reference to the same object—death—and in expressions whose form precisely parallels that of the arpagmos remark in Phil 2:6.
What he [Eusebius] wants to say, rather, is that because of the hope of salvation crucifixion was not a horror to be shunned, but an advantage to be seized.
“Arpagma” is used exactly this way in Hist. Eccl. VIII,12.2. At this point Eusebius is recounting the sufferings of Christians in periods of persecution. Some believers in order to escape torture threw themselves down from rooftops. There can be no suggestion of “robbery” or of violent self-assertion in this remark, nor can self-inflicted death under such circumstances be considered an unanticipated windfall.
Roy W. Hoover, Harvard Theological Review (1971) 95-119, pg. 108