In most cases, this error means you've installed the EA on a symbol of your broker that's not tradable. Some brokers use suffixes on their tradable symbols, such as EURUSD.a instead of EURUSD. In this case, you need to install the EA on a chart of a tradable symbol (in this case, EURUSD.a) and also set the 'Symbol Suffix' parameter to .a to solve this issue. You may be confused as to why brokers do that. In some cases, brokers need separate trading pairs for indicative purposes (e.g., to calculate technical info, like your deposit load and margin level) and another set of pairs to be traded. In this case, they do it by making two sets of pairs - indicative ones without the suffix and tradable with it.