If you are a daily Bitcoin user who sends and receives coins frequently chances are that you have run into a transaction that didn’t confirm immediately the next block. There are two main reasons why a Bitcoin transaction may not be confirming, the first is that the transaction is invalid and was created fraudulently, since the signature doesn’t math with the corresponding key the network rejects the transaction all together. The other most common reason that a transaction isn’t confirming is because the sender sent too low of a miners fee.
Conclusion
If your transaction isn’t confirming it is most likely because the miner’s fee is set too low. First check that the miner’s fee specified is higher than the minimum relay tx fee which is 0.0001. If it is, then make sure that the transaction properly propagated through the network by checking block explorers like blockchain.info or blockr.io. If the transaction doesn’t displays on the block explorers and shows as having 0 confirmations on your wallet or local node, then use Coinb.in to rebroadcast a transaction that will get picked up by another node and relayed. If the transaction has already been relayed then unless you set the opt-in rbf flag you will have to wait it out.
http://themerkle.com/education/why-is-my-bitcoin-transaction-not-confirming/
