The error message says: "550 Free users can upload 50MB each time. To resume, please log off and log on again AFTER 2 minutes."
Here, 550 is just an FTP response code. So the real meaning is "Free users can upload 50MB each time". Each time means each continuous logon. If you log off and immediately logon again, it will be considered the same logon. You need to log off and wait for a while before you logon again.
You can also use DriveHQ FileManager client software. With FileManager, you just need to click on Ok to resume. There is no need to wait.
Anyway, DriveHQ service is optimized for businesses. You can use our free service, which is designed for personal and casual users only. If it is for business, please upgrade to a paid account. The price actually starts at only $1.99/month now! Annually, you can save additional 2 months for only $19.99/year.