There were several instances in the 16th Century where the traditional Latin vocabulary used by St. Jerome in the Vulgate was challenged based on the grammar and vocabulary in the Greek New Testament.  Most of this were minor quibbles of no great import, but some were used by Protestants to question Catholic teaching and practice.  The three most important challenges were the following:

1) The translation of "metanoeo" as "paenitentiam agite"The Greek verb "metanoeo" comes from two other Greek words: meta (change) & noos (mind).  The most accurate rendering into English of the meaning of this word would be "to repent."  The implication was that at some point in time someone would change their mind about a past action and regret having done it.  There was no simple Latin equivalent of this Greek term and so the Vulgate used the phrase "paenitentiam agite "which in Latin means "do penance."  The idea of "penance" in Latin carried the connotation of regret and sorrow for past actions but went further in that it also implied the performing of acts of reparation and mortification.  By having Jesus say that his followers had to "do penance and believe the Gospel" (Mark 1:15) it implied that they needed to perform acts of mortification (fasting, self-denial, wearing a hair shirt, self flagellation) or reparation (restoring loss goods, compensating victims) , as conditions for the forgiveness of sins.

The Protestants in the 16th Century claimed that the word "metanoeo" carried no such implication and that all that was needed was a genuine sense of sorrow for sin.  Certain radicals – typified today by some Dispensationalists – even stated that sorrow for sin was not needed.  They claimed that repentance merely meant that you intellectually changed the way you thought from that moment forwards without any reference to past actions.  Those were "covered over" by Christ and hence forgotten by God.  Technically, the Protestants were right.  The words "metaneo" and "paenitentiam agite" are not exact equivalents.  But they forgot that the NT uses Greek words in a distinctly Hebraic way and that they must be understood in the context of a Hebrew idiom.  The word for "repent" in OT Hebrew was "nacham" which has the following connotations according to Strong's Concordance:Nacham – to be sorry, console oneself, repent, regret, comfort, be comforted a) (Niphal) 1) to be sorry, be moved to pity, have compassion 2) to be sorry, rue, suffer grief, repent 3) to comfort oneself, be comforted 4) to comfort oneself, ease oneself b) (Piel) to comfort, console c) (Pual) to be comforted, be consoled d) (Hithpael) 1) to be sorry, have compassion 2) to rue, repent of 3) to comfort oneself, be comforted 4) to ease oneself.

As you can see, the OT concept included sorrow, grief, compassion, and acts to comfort others and be comforted oneself.  Repentance was not merely an passive act of regret nor merely a change of mind.

As such, St. Jerome's choice of "do penance" had the wider context of the OT meaning in mind and we need to appreciate that.  In later rabbinical theology, the term "teshuvah" (turning) would be used for repentance.  It would be defined by the Talmud as a turning towards God and a turning away from one's sins.  It also meant a turning towards one's sins as something to contemplate and regret: the opposite of moral denial.  St. Thomas Aquinas was aware of this rabbinical teaching and in his Summa Theologiae he has the turnings towards God and towards/away from sin as two of the four results of the grace of justification.  (The other two were the forgiveness of sin and the infusion of the new life of grace.)  The Rabbis were not heavily into acts of mortification. Many of these practices were unique to Christians who wished to imitate their Lord in his suffering for mankind on the cross.  Nevertheless, repentance in "sack cloth and ashes" was a Jewish practice advocated in both Testaments(e.g., Daniel 9:3, Matthew 11:21).

In summary, the issue here was whether Greek grammar or the Biblical idiom should guide the translation.  The Protestants opted for the former while St. Jerome and the Catholic Tradition opted for the latter.

2) The translation of "kecharitomene"as "gratia plena" King James Version – Luke 1:28 And the angel came in unto her, and said, Hail, [thou that art] highly favoured, the Lord [is] with thee…Douay-Rheims Version – Luke 1:28 And he came to her and said, "Hail, full of grace, the Lord is with you!" In the Greek NT, the term "kecharitomene" is applied to Mary at the Annunciation.  It is the perfect passive participle of the Greek verb "charitoo" which has the following meanings according to Strong's Concordance: 1) to make graceful a) charming, lovely, agreeable 2) to peruse with grace, compass with favour 3) to honour with blessings.

Once again, the 16th Century Protestants interpreted the Greek text very literally and insisted that kecharitomene did not mean "full of grace" but rather "highly favored."  They felt that the phrase "full of grace" exaggerated the Angel's greeting and carried improper implications which had led to "excessive" Marian doctrines such as the Perpetual Virginity, Mary's Indefectability, and the Immaculate Conception.  The perfect passive participle in Greek is the superlative form of comparison.  It is not merely "highly favored" but "MOST highly favored" And the Greek word "charis" is the word used for grace in the NT. It literally means "gift".  This is actually another debate for Greek vs. Latin grammar.  Does "charis" refer to the passive reception of God's favor or an active power granted to man?  Here the Protestants claimed that the reception of the gift of grace did not require a response.  This despite the very clear teachings of the NT:

In any case, "kecharitomene" in reference to Mary means that she already was the most highly "graced" person before Gabriel had come to her.  He was recognizing a past completed action which had been accomplished long before.  The distinction between "most graced" and "full of grace" is notional at best.  And in line with the OT teaching, having been "most highly graced" Our Lady responded to God's call having been first empowered by His gift.  As Jesus himself would say later in Luke's Gospel, she did not only hear the word of God, she kept it (Luke 11:28).  So once again, St. Jerome did not restrict his translation to a mere literal rendering of words, but he chose a dynamic equivalent to convey the full Biblical meaning.  No other human being is ever called "kecharitomene" in the Bible.  It is a unique title for the Mother of God.  It was not a merely passive favor but an active empowering which manifested itself in works faithful to the plan of God.  In light of this, it is entirely legitimate to see this term as consistent with Mary possessing the special pre-existing qualities which the Catholic Church proclaims in the Marian dogmas.

3) The translation of "dikaioo" as "iustificare".  This was a very critical challenge.  Luther et al claimed that the Greek verb "Dakaioo" meant a forensic declaration of innocence by God.  It did not make the recipient just but merely considered him to be so in a legal sense.  This is similar to the idea that a man is considered innocent in the legal sense until you prove him to be guilty.  The Latin word "iustificare" had the connotation of making someone just in an active way by correcting their faults.  This grammar challenge was critical to the whole Deformation program.  The Protestants claimed that one is declared just before God on the basis of a trusting belief in Jesus ALONE without any need for an active volitional response.  Once again, a merely literal rendering of the Greek word "dikaioo" does have a predominantly forensic character, but it does not exclude the idea of making righteous.  In his commentary on Romans, Fr. Joseph Fitzmeyer documents that even in the 16th Century, Greek grammarians knew that "dikaioo" was not a purely forensic term.  In fact in context, St. Paul made it clear in his writings that justification was not merely being declared righteous but being made so:

So once again, St. Jerome and the Vulgate are vindicated by giving primacy to the context of the Biblical idiom over the alleged meanings of abstract Greek definitions.  The Catholic Tradition is shown to be a more faithful conveyor of Biblical truth than mere pagan grammar.