The problem is that Ajax is inherently dangerous as it relies too much on user input.
If you use the MuteScreamer plugin you need to exclude some of the items or set the threshold higher so people won't get locked out. Better to have some protection than none at all.
If you're wanting more protection, try installing ZBBlock. Be warned it's not a plugin, so it takes a bit of knowledge, time, and patience to install/setup.