Yes.. definitely something gone wrong.
Use ethernet for the first backup.. you can do it in complete isolation to the rest of the network. Just reset the the TC and plug it into the computer with ethernet.
I would recommend you erase the disk and start over.. although TM can pick up where it left off.. this first backup is the most crucial one.
It should take 4-5 hour max on ethernet.
Once that is complete you can go back to using wireless with incrementals.
Thanks for the advice, after following your suggestion the TC backed up the whole thing. I did however managed to figure out the reason why it wasn't backing all the way is because of Legacy filevault was on. after turning it off and turning on filevault 2 and using the backup up with encryption it worked!