So I fixed my problem. Here's how:

    a:4:{
	    i:0;s:23:"bandpress/bootstrap.php";
	    i:3;s:56:"posts-from-single-category-widget/post_from_category.php";
	    i:4;s:15:"something else ";
	    i:5;s:68:"syntax-highlighter-with-add-button-in-editor/syntaxhighlighterpp.php";
    }

I figured out every activated plugin is defined between the i and the ;, so by removing the following my error message dissapeared:

    i:4;s:15:"something else ";