Hi Pjilippe,
From what I understand this is an issue can occur when your broker cannot place trades, an invalid symbol, or an account not set up properly. So, did you log into your MT4/MT5 with the master password and not the investor password? Also, some brokers have two forms of chart names, for example, where the chart tab shows on of these two names EURUSD or EURUSD.i (or some other name with a dot suffix). If your broker uses these two forms of chart names contact your broker to make sure which form you are to use. The first thing I would suggest is to close your terminal and log back in with the master password and make sure you are using the correct chart name. Then try to place a small trade manually when you know the market is open.
Let me know how it goes!
Alan,