Fixed: “MTP Device” keeps popping up

I struggled for some time with a Samsung Galaxy S (Android cell phone). Connected via USB to my PC with Windows XP, it does not work: the PC continuously discovers a new “MTP Device” but the device never works (error code 41). The problem seems to be fairly common, but the solutions found online did not work. Moreover, the problem does not seem to be limited to this particular device: it seems to be spread over many devices that expose a Media Transfer Protocol inteface (MTP indeed).
Taking a look at setupapi.log, we see that the device class is EEC5AD98-8080-425f-922A-DABF3DE3F69A.
Open the register, go to HKLM\SYSTEM\CurrentControlSet\Control\Class\{EEC5AD98-8080-425f-922A-DABF3DE3F69A} and we note that there is an UpperFilter, KLFLTDEV. Too bad that this device does not exist .. seems to be a remnant of an old Kaspersky installation. Deleted the UpperFilters key, the problem is solved without even the need to reboot.