Calvin: A right understanding of the Lord's Supper is a requisite for salvation?

Over on the CARM boards a Roman Catholic posted the following:

Council or Protestant Reformer? Here's a little quiz for your Thursday afternoon. Please identify the author of the following doctrinal quotations. Is it from a Catholic Council or a Protestant Father?

What followed were a series of quotes with two choices: a Roman choice, or a Protestant choice (all the quotes though were from Protestants). The goal appears to be to demonstrate that certain historically important Protestants held to particular Roman beliefs. This sort argument really is, in essence, futile. Protestants don't follow earlier Protestants as infallible interpreters. Nor is it surprising to find that the earliest generation of Protestant reformers may have still held to particular Roman beliefs on various things. Roman Catholics are quick to point to an infallible "development of doctrine" to explain their inconsistencies with earlier periods of church history. It's a double standard then to demand that Protestant doctrine did not (or could not)"develop" further away from Romanism as history progressed. So, while some of the quotes accurately reflected the beliefs of the Protestants being cited,  some of them were historically misleading, and when placed back in context said something much different than what the Roman church believes.  I'd like to highlight a few of these quotes in a few blog entries. Here's the first quote and choices:

1. A right understanding of the Lord's Supper is a requisite for salvation
“As the holy sacrament of the Supper of our Lord Jesus Christ has long been the subject of several important errors, and in these past years been anew enveloped in diverse opinions and contentious disputes, it is no wonder if many weak consciences cannot fairly resolve what view they ought to take of it, but remain in doubt and perplexity, waiting till all contention being laid aside, the servants of God come to some agreement upon it. However, as it is a very perilous thing to have no certainty on an ordinance, the understanding of which is so requisite for our salvation, I have thought it might be a very useful labour to treat briefly and, nevertheless, clearly deduce a summary of what is necessary to be known of it.'

a. Council of Trent
b. John Calvin

The quote appears to have the polemical value of demonstrating that while contemporary Protestants supposedly do not think a correct understanding of the Lord's Supper is all that important, Calvin says it is important and "requisite for salvation." The underlying assumption is that Rome teaches a correct understanding of the Lord's Supper is requisite for salvation.  Well, if this is what this question is supposed to imply, a staff apologist from Catholic Answers stated 70% of Roman Catholics do not understand the Eucharist.

Here is the document this Calvin quote is taken from. When Calvin implies a right understanding of the Lord's Supper is a requisite for salvation, he's talking about the wrong way of understanding the Lord's Supper being the way Rome understands it. If you scroll through the document, notice Calvin painstakingly details Rome's abhorrent errors. When Calvin finally gets to other Protestant views, he doesn't classify them as he has Rome's understanding. Calvin clearly thinks Rome's view is wrong.

Of Protestants, Calvin goes on to say:

First, I beseech all believers, in the name of God, not to be too much scandalized at the great difference which has arisen among those who ought to be a kind of leaders in bringing back the light of truth. For it is no new thing for the Lord to leave his servants in some degree of ignorance, and suffer them to have debate among themselves—not to leave them for ever, but only for a time to humble them. And indeed had every thing till now turned out to a wish without any disturbance, men might possibly have forgotten themselves, or the grace of God might have been less known than it ought. Thus the Lord has been pleased to take away all ground of glorying from men, in order that he might alone be glorified. Moreover, if we consider in what an abyss of darkness the world was when those who have shared this controversy began to bring back the truth, we shall not wonder that they did not know every thing at the beginning. The wonder rather is, that our Lord in so short a time enlightened them that they were themselves able to escape and draw others out of that sink of error in which they had been so long immersed. But no better course can be taken than to show how matters have proceeded, because this will make it appear that people have not so much cause to be scandalized at it as is commonly supposed.

Calvin then goes on to describe the views of Luther and the Swiss theologians, in a quite evenhanded tone:

Both parties failed in not having the patience to listen to each other in order to follow the truth without passion, when it would have been found. Nevertheless, let us not lose sight of our duty, which is not to forget the gifts which the Lord bestowed upon them, and the blessings which he has distributed to us by their hands and means. For if we are not ungrateful and forgetful of what we owe them, we shall be well able to pardon that and much more, without blaming or defaming them.

What's interesting to me about this document from Calvin is that he doesn't completely throw Luther and Zwingli under the bus. Rather, he points to their contributions against Romanist error, and explains what he feels were their shortcomings. Calvin looked forward to a day in which "concord" would be "fixed" among the Protestant leaders. He doesn't appear at all to be saying in this document that either Lutherans or Zwinglians lacked salvation because of their view of the Lord's Supper. The point again is that the incorrect view of Lord's Supper, the view that if held is against salvation, was, for Calvin, the Roman Catholic view.