If all of your Waves placed in orders or leased and you don't have enough Waves for the fees in this case, you can't create a new order because your funds are occupied in open orders or leases. Also, if you do not have Waves and you have opened order to purchase initial Waves until the order is not executed you will not be able to open a new order.
Please click on the Cross icon (X) to remove some of your open orders or cancel some open leases and release the funds.
For more information please follow the instruction How to trade tokens on the DEX
Customer support service by UserEcho