What does 2 Corinthians 7:11 mean?

Somewhere between the writing of what we now call "1 Corinthians" and "2 Corinthians," Paul composed a severe letter to the same church, which is now lost. In it, he apparently rebuked them for not dealing with at least one person among them who stood against Paul during his last visit with them. He instructed them to hold this person accountable, which they have now done (2 Corinthians 2:6). Paul has received news from Titus, who delivered the letter, that they have experienced great sorrow over their sinful lack of response to this man and have repented. Paul called this sorrow they felt the "godly grief" that brings about repentance.

He now points to some other things this sorrow has caused. The Corinthians have reacted to it with an earnestness and eagerness to clear themselves by making things right. They have responded with indignation towards Paul's opponent. They have expressed "fear, which in this context is reverence for God and or respect for His punishment.

The Corinthians have expressed longing for Paul, enthusiasm instead of passiveness, and loving punishment of Paul's sinful opponent. Paul declares that in all these ways, they have proved themselves innocent.

It's not exactly clear how Paul means they had proved "innocent" if, in fact, it was a sense of guilt which brought them to sorrow and the repentance that followed. Most likely, Paul means they have re-established their innocent standing now that they have dealt with the sins which made them guilty.