Changing Masteries Causing an Error

Simply put, i cannot change my masteries at all. Attached is a photo of the error message that I receive, even though the photo is not mine, meaning I am not the only one who has received this error. I cannot change my masteries, ever. I cannot alter them, nor can i go to another page to even look at it. This occurs both in champion select, and in the profile. I don't mean to be vague, but there's not much i can really say about it. The glitch started when I saved a mastery page at the last second before I got into a game. That game, it didn't give me any masteries, and the masteries weren't saved at all, but when I tried to recreate said page, this error started popping up. I don't think any logs apply here, but if you need any I will do what i can to get them for you. For now, i can only play Taric support until this is fixed... so that'll get pretty old.