Thank you for posting the error message!
But so far I have no good what could cause the problem. The most common reasons for that problem are some difficulties with the Permalink scheme or the .htaccess file.
However there were a few report of situations in which other plugins made trouble. That is why we should find out whether one of your other plugins interferes somehow. When which plugin, I can try to find out what is wrong and how to fix it.
In my opinion the best way to find out is that you activate the statistics feature temporarily again and then deactivate the other plugins one by one, reload the page and try to download one file. You may of course activate the other plugins afterwards.