I have -1 confirmations for an inbound transaction on my Electrum wallet. What does is it mean to have -1 confirmations?
It is a known bug, just restart the client and/or switch to another server in the Network window (green dot in the bottom right).
If this doesn't fix the 'Unverified -1 confirmation error' try deleting the block_headers folder on your Electrum directory -> https://bitcointalk.org/index.php?topic=330626.msg5292794#msg5292794
It probably means, it did not synchronize properly yet, and does not know how many confirmations there are