In case anyone who has sent trackbacks to one of my posts and not received an acknowledgment from me (as I like to do) or have not seen your trackback on the respective post, please leave a common on the post you sent the trackback to saying so.
The Simple Trackback Validation plugin was doing too good a job at stopping spam trackbacks that it stopped all of them. I just changed the options to not verify the IP address and tested the trackback function thoroughly and it now works correctly once again.
Thanks and sorry about that. 
