Okay, I think I know what's happening, you need to delete that transaction from the core, as it seems to have already dropped from miners memory pools but since it is still showing up in your wallet, core won't let you make another transaction until that one is deleted, close the core and do this in terminal:
C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe -zapwallettxes
Too late, I see,, sorry..
Remember it for the next time, since you're running core.