I don't think the transaction I am referring to is listed there. I had an incoming and outgoing transaction of the same amount (2.44) in that wallet yesterday, but this is a third and separate one. Here is all the info my wallet tells me about this specific transaction:
Status: 0/unconfirmed
Date: 4/1/2013 14:22
From: unknown
To: 15s17qYWvj9vTJrjKnywGPiduM7NvbhNx7 (own address)
Credit: 2.439 BTC
Net amount: +2.439 BTC
Transaction ID: 2176854c0ed2e2a8e6c2f4aeb429e4548452ba59088cc63ff36634cdeae062a4
It looks as though blockchain doesn't see that transaction ID at all.... Thanks for your help so far!
OK, so this is an incoming transaction to you?
If so, the the party that sent it needs to re-broadcast it as your client knows about it but the rest of the network does not.
To clear this, simply close your client and re-launch. The memory pool will not have this transaction in it.
(The only exception there is if someone was cheating you, that transaction still existing in your memory pool might be evidence and shutting down your client would cause any trace of it to disappear.)