Mining Dutch wasn't supposed to be selectable for Pool Balance as the implementation isn't ready yet. They do have an API for balance, but it must be requested for each individual coin (can be 50 or them...) so Awesome Miner will put quite high load on their servers to figure all this out.

I've reached out to them about this now and see if there are any good solutions. The plan is to have support for balance via Mining Dutch later on.

Once the implementation is ready, the idea is that you enter your Mining Dutch API-key (can be found in the account settings on the Mining Dutch web site) in Awesome Miner.