So, the argument you're referring to, paraphrasing the sep article, is:

1. Consider a being than which no greater can be conceived.
2. If such a being fails to exist in reality, then a greater being - namely, a being than which no greater can be conceived, and which exists in reality - can be conceived.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must exist in reality.

We are implicitly speaking here of a set of beings-that-can-be-conceived, which we can call S. The fallacy here is an equivocation between two different conditions of a being.

Condition A. We can conceive that the being exists-in-reality

Condition B. The being actually exists-in-reality

Let's restate the argument in clearer terms, without equivocating:

1. Consider a being than which no greater can be conceived.
2. If such a being lacks Condition B, then a greater being - namely, a being than which no greater can be conceived, and which has condition A - is in S.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must have Condition B.

The clarified argument falls flat, because the being of step 2 is not necessarily greater than the being of step 1. Even assuming the being of step 1 lacks Condition B, it may still have Condition A, just like the being of step 2.

Now, we might try to fix the argument by resolving the equivocation in a different way, so that the being of step 2 has Condition B instead of condition A:

1. Consider a being than which no greater can be conceived.
2. If such a being lacks Condition B, then a greater being - namely, a being than which no greater can be conceived, and which has condition B - is in S.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must have Condition B.

But still it falls flat, because now we can't guarantee that the being of step 2 is in S at all; it would have to actually exist-in-reality, and we have no way to establish that.

So either way we resolve the equivocation, the argument doesn't work.

So, the argument you're referring to, paraphrasing the sep article, is:

1. Consider a being than which no greater can be conceived.
2. If such a being fails to exist in reality, then a greater being - namely, a being than which no greater can be conceived, and which exists in reality - can be conceived.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must exist in reality.

We are implicitly speaking here of a set of beings-that-can-be-conceived, which we can call S. The fallacy here is an equivocation between two different conditions of a being.

Condition A. We can conceive that the being exists-in-reality

Condition B. The being actually exists-in-reality

Members of S might have any combination of Condition A and Condition B. They might actually exist in reality, and we can conceive of them existing in reality (such as the moon). They might actually exist in reality, but we can't conceive of them existing (who says the human mind is capable of grasping everything in the universe?). They might not exist in reality, but we can conceive of them doing so (such as leprechauns). They might not exist in reality, and we can't conceive of them doing so.

The equivocation is over whether the being in step 2 of the argument has Condition B (exists in reality) or Condition A (we can merely conceive of it existing in reality). Let's restate the argument in clearer terms, without equivocating:

1. Consider a being than which no greater can be conceived.
2. If such a being lacks Condition B, then a greater being - namely, a being than which no greater can be conceived, and which has condition A - is in S.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must have Condition B.

The clarified argument falls flat, because the being of step 2 is not necessarily greater than the being of step 1. Even assuming the being of step 1 lacks Condition B, it may still have Condition A, just like the being of step 2.

Now, we might try to fix the argument by resolving the equivocation in a different way, so that the being of step 2 has Condition B instead of condition A:

1. Consider a being than which no greater can be conceived.
2. If such a being lacks Condition B, then a greater being - namely, a being than which no greater can be conceived, and which has condition B - is in S.
3. But the being of step 2 is a contradiction, because nothing can be greater than the being of step 1.
4. Therefore, the being of step 1 must have Condition B.

But still it falls flat, because now we can't guarantee that the being of step 2 is in S at all; it would have to actually exist-in-reality, and we have no way to establish that.

So either way we resolve the equivocation, the argument doesn't work.