Tamas - here is how to reproduce it. 1. go to the Ducascopy data dropdown, 2. Add new symbol, 3. Add EURUSD 3 times so you will have EURUSD, EURUSD(2), and EURUSD(3).
Then delete them all. Then try and do it again and it should throw an error for you because they already exist except they really dont.
Can you describe step by step what you did to reproduce this issue ?