Quote from: pooya87 on January 13, 2019, 05:24:27 AM

in short you are trying to spend bitcoins that you don't own.

in other words you are spending a transaction output that doesn't belong to your key. maybe that transaction wasn't confirmed, or double spent and became invalid,... i can't tell without having more information but one thing is for sure, your transaction that you are trying to broadcast is invalid that is why it is being rejected.

go to your wallet, in history tab, and see if you can see any transaction that is marked unconfirmed or local. and see if you can find a transaction that starts with 426b28... it seems like this is the tx you are trying to spend and fail to do so.

Yes there is a transaction that starts with 426b28.., and yes, it still hasn't confirmed. But I am only spending the bitcoins that are there on my wallet.
Why is this problem occuring then?
What to do now?