php Illegal string offset with similar_text function

I used wordpress 4.3.1 with php 5.6.14 version. I used this source code with my plugin:

$original = $wpcopy_options['option'];
$rewriten = $wpcopy_options['rewrite'];
$output = similar_text($original, $rewriten, $result);

I got this error:

Warning: Illegal string offset 'option' in C:\xampp\apps\wordpress\htdocs\wp-content\plugins\... on line 15

Warning: Illegal string offset 'rewrite' in C:\xampp\apps\wordpress\htdocs\wp-content\plugins\... on line 17

via Chebli Mohamed