Do you have any orders open or pending? Funds that are used in an open or pending order cannot be withdrawn.

Solution: cancel the open orders.

Do you have the currency available in your Kraken account? Although you may see the total amount held in your account, you may have it selected where your account shows the total sum of all of your currencies shown in a specific currency, though all of your currencies held are treated separately.

An example is if you hold both Pound sterlings (GBP) and eurozone euros (EUR) in your account, you can't withdraw the total amount in a single US Dollars (USD) withdrawal.

Solution: exchange your balances to the currency you want to withdraw.

Do you have any open spot positions on margin? Spot positions on margin require collateral and that collateral cannot be withdrawn while the positions are open.

Solution: close the open spot positions on margin.

Do you have a negative balance in any currency? This will prevent withdrawals from your account.

Solution: deposit funds in the currency that has a negative balance or exchange other currencies to make up for the negative balance.