Addons.SetAddonEnabled can’t disable Aerial addon

Hi,
I’m trying to remotely disable the Aerial screensaver using json-rpc and curl.
The addon is enabled:

Code:
curl -s -H "Content-Type: application/json" -X POST -d '{"jsonrpc": "2.0", "method": "Addons.GetAddonDetails", "params": {"addonid": "screensaver.atv4","properties":["enabled","name"]}, "id": 1}' http://remotecomputer/jsonrpc

gets answer:

Code:
{
        "id": 1,
        "jsonrpc": "2.0",
        "result": {
                "addon": {
                        "addonid": "screensaver.atv4",
                        "enabled": true,
                        "name": "Aerial",
                        "type": "xbmc.ui.screensaver"
                }
        }
}

but when I try to disable it by making

Code:
curl -s -H "Content-Type: application/json" -X POST -d '{"jsonrpc": "2.0", "method": "Addons.SetAddonEnabled", "params": {"addonid": "screensaver.atv4", "enabled":false}, "id": 1}' http://remotecomputer/jsonrpc

I get

Code:
{
        "error": {
                "code": -32602,
                "message": "Invalid params."
        },
        "id": 1,
        "jsonrpc": "2.0"
}

while doing the same but setting “enabled” to true gets

Code:
{
        "id": 1,
        "jsonrpc": "2.0",
        "result": "OK"
}

I’m completely in the dark, if anyone could help me…
Thanks in advance.