The send relies on several APIs. An error will occur if one of them is down. Please try again after a few hours.
After you send, open Blocktrail or Blockchain.info to monitor the transaction
It is prone to remain unconfirmed for a while
Transactions take time to confirm. Several hours is normal; even days in extreme cases. Including higher miner fees may help speed this up.
Please be patient. Don't worry, as long as you can view the unconfirmed transaction on any site, it will get confirmed eventually
If you want to sweep several assets, you should wait for the first to confirm before you sweep the second
The 'BTC Dust' is the amount of Bitcoin to send along with the asset. If you want to empty the paperwallet completely, it's a good idea to increase the dust such that dust+fee equals the address' bitcoin balance