If you get a warning like this:
'Warning: array_keys() [function.array-keys]: The first argument should be an array in /homepages/20/d108879515/htdocs/Relationship_blog/wp-content/plugins/adsenseoptimizer/adsenseoptimizer.php on line 17'
The reason for this is usually that you use a ad type, but specified no sizes for this ad type. Check which ad types you use in your blog (in the yellow section), then scroll up to the blue section and check if all of the used ad types have at least one tick at the sizes you can choose.
in version 3.1. this warning will be removed. nevertheless you should choose a size for your ad.