Try to check the port setting within the router. Different router may have different port setting rule. Basically, when in passive mode with non standard ftp port(port 21), you need to set all the opened ports within the router setting. For example, if you set port to 40000 instead of using the standard ftp port 21, and passive port range from 50000~50003, then you need to open port 40000, 50000~50003 within the router. Some router allow to set a port range that make the opened port setting more easily but some of them need to set those port one by one. Good Luck.