Transactions on the blockchain can be rejected by miners if the proposed transaction fee was too small or if you run out of gas (Ethereum).
To determine reason of the rejection, first go to cryptocurrency with rejected transaction in BC Vault application, then click on "View all transactions" under "Latest transactions":
Click on a transaction that was rejected and on the presented "TRANSACTION DETAIL" dialogue click on the "Transaction hash" to copy it:
Now you have copied the ID of the rejected/failed transaction and you can lookup transaction details on blockchain explorer for particular cryptocurrency (in our example we will go to Ethereum blockchain explorer at etherscan.io) and after copying in the transaction id we get all the details:
In this transaction the reason for rejection was that transaction run "Out of gas". With ERC20 tokens it might happen, that the default Gas Limit of 100000 is not enough and in this case you have to use higher limit of 150000 or even higher.
Try to do the same transaction with a higher transaction fee (or gas limit in case of ETH transaction rejection due to "Out of gas").
Generally speaking blockchain explorers will always tell you why your transaction was rejected.