Deactivate GeoIP auto-updater / HTTP 500 error


after installing version 1.10.1 to a Windows 2008 R2 machine with IIS 7.5 and MySQL 5.5, which btw. was really easy and went smoothly, I had the problem that one day visits would not get recorded anymore all of a sudden.
Using Fiddler I saw a HTTP 500 error on /piwik.php?action… when our web page was loaded in the browser. Thought of a security related problem because I (might have?) changed the file security rights on the wwwroot directory recursively. Since I could not find anything on the web I deleted and reinstalled Piwik, restored the connection to MySQL and the Piwik configuration files and it was working again.
But after all I saw the problem today again and found a workaround - thinking of a “security breach” I tracked the last visitor (5 days back) and found a file that has exactly the same time stamp : GeoIPs database file /piwik/misc/GeoIPCity.dat with a size of 0 KB - but hey, I do NOT use this file (name), our GeoIP (PHP) data base file is named /piwik/misc/GeoLiteCity.dat which is still there ( ~18MB ). After deleting the empty file Piwik is working like charm again.
Maybe this is due to an auto-updater configuration within Piwik, which I played with a few weeks ago, but discarded (empty in the web configuration, but the radio button is still set to weekly); I scripted it myself and this script is working perfectly.

My question is : where is the auto-updater configuration located so I can manually delete it (in the .ini files)?

UPDATE : It happened again tonight; seems to “break” at exactly the same time someone calls the web page page/Piwik. Changed my script to rename the GeoIP data base from GeoCityLite.dat to GeoIPCity.dat which is also working to find out if the problem persists.