Problem with model

I tried to make a fire with a model like this

PHP Code:

function getByUsername($username)
{
return $this
->select('id')
->where('username',$username)
->asObject()
->first(); 


Running normal on localhost (linuxmint, php7.2), but in vps (centos, php7.1) error and display message 
"whoops! we seem to have hit a snag. Please try again later"
can someone explain this?