There are two oil lights. One is to tell you it's time for a (ridiculously early) oil change and is reset by pushing a slim probe through the dashboard 'glass' via a rubber plug ( which is easy to push inside and lose forever), and the other is to warn you of too much or too little oil in the engine. This one usually fails and then flashes continuously.
It's sender sits inside the engine sump and consists of a float connected to a switch. The height of the oil level and thus the float either switches the flashing sequence, nothing, or 'on' continually. It is THAT sensor arrangement that is faulty.
You need to pull the sump off after draining the oil and replace or possibly repair/clean the float and switch arrangement... Or ignore it!
Jon
May 2009