I have had this error and more recently I have received:
There is an error. Please report the message (Piwik 2.4.1) and full backtrace in the Piwik forums
Warning: rename(C:\piwik/misc/GeoIPCity.dat.new,C:\piwik/misc/GeoIPCity.dat) function.rename: The proces cannot access the file because it is being used by another process. (code: 32) in C:\piwik\plugins\UserCountry\GeoIPAutoUpdater.php on line 268.