Check your configuration, User Registration Profile Options => Avatar Directory should be set to images/avatars, seems to be empty on your end...
Can you translate the error message?? I don't know what the problem is.
MyBB find error, no continuing.
I still don't know what the MyBB error is. You need to translate the error message you gave a screenshot for into English.
There is no special thing to translate.
Its just telling;
MyBB has experienced an SQL error and cannot continue.
@ OP, try to CHMOD ./uploads/avatar/ Directory.
AdminCP>Settings>User Registration Profile Options>Avatar Directory
What do you have for the above setting? The problem is due to the above setting so you need to tell us what you have there.
Use lowercase letters, like
uploads/avatar