Do you have the value of the particular assets you are looking to withdraw available in your Kraken account? You might see the total account value held in your account displaying under one default currency, but this could be a combination of several different assets, which you are only able to withdraw individually. An example is if you hold both Bitcoin (BTC) and Ethereum (ETH) in your account, you can't withdraw the total amount in one Litecoin (LTC) withdrawal.
Solution: exchange your balances to the currency you want to withdraw.