Unknown error during task verification?

Hey guys, I'm getting an "Unknown error during task verification" in intellij - code is good, passing all requirements at codegym website, but it seems i can't verificate it using intellij - anyone knows what's wrong? Level 3, lesson 3, below, please find a code I'm using.

package pl.codegym.task.task03.task0302;

/*
Wyświetl od razu
*/
public class Solution {
    public static void printString(String s)
    {
        System.out.println(s);
    }// tutaj wpisz swój kod

    public static void main(String[] args) {
        printString("Cześć, Amigo!");
    }
}