That is not an error. The system has a built in system to detect flood (when a lot of images are uploaded from the same IP) and you are not logged in.
This system can be tweaked in includes/config.php (just look for "flood") so you can increase or decrease the limits based on daily, week and month uploads. You can also disable the whole system.
Now, you are getting the flood detected because you have uploaded a lof of images and you wasn't logged in as admin. The system can't tell that you are admin if you don't log in. So you can simply increase the limits or disable the system.
Cheers.