TOPIC: I was told the following two sentences are both correct

I was told the following two sentences are both correct.
1. We agreed that no action should be taken.
2. We are agreed that no action should be taken.
Can the verb 'agree" be used in passive voice? What's the differnet in meaning between the two?

Yes, both these sentences are correct. THe reason is as follows:
In the first sentence,"agreed" is a verb meaning to accept or have the same opinion on an idea.
In the second sentence, "agreed" is an adjective which can be used with a BE verb to mean "X and Y are of the same opinion or accept the same idea".
So, in fact, there is little real different in meaning between the two constructions, but one (#1) has more sense of action, while#2 has more a sense of status description (i.e., the agreement has already been concluded). So, when you want to express the action of agreeing, choose #1, and when you're reviewing what action has already occured, choose#2 to describe the situation.