Function name must be a string in views_php/plugins/views/views_php_handler_field.inc on line 185

I have 7.x-1.x-dev of the module installed. I created a view which has a php field with some calcuation in the value part. I Selected "sort numerically" in enable click sort. I started error message in the error logs as

Function name must be a string in views_php/plugins/views/views_php_handler_field.inc on line 185

Thanks,
Sadashiv.