PHP - Input string was not in a correct format error

I'm using laravel and this :

https://github.com/comodojo/metaweblog/

Here is the code in controller:

public function testNewPost() {
    $mwlog = new MetaWeblog("http://example.org/services/metablog.ashx","user","pass");
    $struct = array(
        'title'             =>  "Test Post",
        'description'       =>  "Test Post description",
        'post_type'         =>  "post",
        'categories'        =>  array('uncategorized'),
        'mt_keywords'       =>  array('test','post'),
        'mt_allow_comments' =>  "open",
        'mt_allow_pings'    =>  "open"
    );

    $post = $mwlog->newPost($struct);

}

But it returns :

Input string was not in a correct format.

What's wrong?!

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