Disallowed Key Characters. I can't update or save in expression engine.

Hello There!

Its been a while since I don’t post here. The situation is this. I am trying to update the content of some translations inside an extension (biber multilanguage) using EE 2.5.3 here,

the problem is that everytime I do want to save my changes I am getting the following error:

“Disallowed Key Characters”

does anyone know what does it stands for and how can I fix this asap please 😊

I ll really appreciate your help on this.

btw I ve tried both in firefox and chrome with similar results, I ve also cleared the cache and nothing..

any point would be nice

thank you!