You need your first coins for activating your account
Now, this is where things start to get a little complicated. It’s very confusing to new people, but you need to send and receive at least 1 BURST coin in order for your account to become ‘active’, and thus able to mine on a pool. When you were solo mining, you didn’t have to worry about this, and you made coins that way, then when you assigned your reward to the pool it sent a coin, and your account was activated without you ever knowing it needed to be… But now, with the difficulty so high, it’s very hard to mine any coins solo, and thus you must go about activating your account in a different fashion. My suggestion is to check out one of the burst faucets (if they are fixed, that is) and have them send you a couple BURST. The faucets are the following.