Loco Error: Ajax failure for save

Hi @timwhitlock.
Could you help me, please?
(Don′t know if it goes in this conversation.)
I have used loco in other server and it works great. But i have problems in this server.
So, i have similar error in few sites.
When i try to save a translation i recive the next error:
“Error: document.documentElement.className = ‘js’;”
All sites are on same server.
So i think there is some misconfiguration on it.
When i change theme to twentyseventeen i recive this:
“Error: (function(html){html.className = html.className.replace(/\bno-js\b/,’js’)})(document.documentElement);”
Thanks a lot for your support.
Best!
G