The function involved attempts to read the meta file for the current document. But there seems to be a bad read. That is, if the function cannot read the file, it creates a new, virtually empty array which will not cause you any trouble. So, the function seems to believe that it has read the meta file but is getting corrupt results. I say this, because you have apparently a new installation, and the errors involved occur at a point in the function where it attempts to convert an older model meta file to a new model. But presumably you already have the new one, since this is a new (up-to-date, I assume) Dokuwiki.
If you have the programming confidence, you can try this. Insert the following at line 365:
file_put_contents('meta.txt',print_r($meta,true));
Then you will have this:
$file = metaFN($id, '.meta');
$meta = @file_exists($file) ? unserialize(io_readFile($file, false)) : array('current'=>array(),'persistent'=>array());
file_put_contents('meta.txt',print_r($meta,true));
// convert $meta from old format to new (current+persistent) format
Access a page from your wiki and then check the wiki's root directory for the file 'meta.txt'. See if it has an array in it, which would be the array apparently read from the meta file. You should be able to tell if it has any relationship to the file you read. The first element in the array should be 'current', so you should see something like this:
Array
(
[current] => Array
(
[date] => Array
(
[created] => 1271190629
[modified] => 1271217403
)
It will also have elements directly relating to the document text.