Can't get around "error 406"

What is "error 406"? It is not allowing me to upload a photo in ANY format. I do not possess the computer talent to get around it, much less understand it.
I cleared cookies twice, no change, other than having to guess at a bunch of old forgotten passwords.
I switched to a Chrome browser and I successfully uploaded a couple pics to a glog thread. Not a fan of Chrome in any way, but if I need to get a pic up, I guess I do what I gots to....