OJS 3.2 users fail

URGENT. Dear I have problems with the registration and modification of users in OJS. 3.2
I cannot self-register or modify existing users.
the error I get is Failed Ajax request or invalid JSON returned.
If anyone knows how to solve this problem, I urgently ask for help.
THANKS

Hi @Gerardo_Ribero,

Is there an associated error in the PHP log?