Will probably be a faulty sensor mate. I had a similar issue where it would throw the check oil level message. Would check and top up if needed and would disappear only to come back a few days later. Check the level and it hadn't moved. All I used to do was open the bonnet for 20 seconds or so and close it again. The message is tied in with the bonnet switch so it knows if you've opened it or not. Just tie in getting it changed at your next service as you will need to drain the oil to do it.
