it takes a long time to load that site
Do you get a table with stats in the end?
When the error with uasort(); occurs, the db request has already ended and the result is of it is an array of data and not is not the value false.
This uasort sorts the array which is made of the db query result. It uses a callback function for that purpose and as the error message says the function seems to be an "Invalid comparison function.". But this message means often that there is a misspelling in the name of the callback function or that this function does eventually not exists.
But all the variations of calling this function are working in my test blogs. That is why I think that this problem is somehow related to the PHP installation on your server. But I can not rule out a problem in your data.
I have no further ideas on how-to call this sorting function differently. But I have implemented a test which checks whether the function is available or not and if the function is not available then it simply bypasses it. This way the error will not occur any more. But the data does not get sorted by they "Total" values.
I have added also a little debug section which should help find the cause of the error. You should see something like that:
sort_downloads_per_media_desc is a method of $this
sort_downloads_per_media_desc is a method of "podPressAdmin_class"
$stats is an array"
there is "total" value for each media file in $stats"
Please, tell whether one of these four value is not "true" in your blog. Which one is it?