We need to be sure which light we are all talking about, I think.
Which light, what colour (amber or red) and is it flashing or solid? Use this diagram for reference:
If it is the oil light (21) then solid red (with three beeps) would indicate a low oil pressure
problem, which would need to be sorted before driving the car again.
Solid amber indicates oil level too low - which means that, like me, you have an oil level/temperature sensor in the bottom of the sump. I was surprised to find this on my car, but the Toledo was the top-of-the-range Seat in 2001 so I suppose they got all the bells and whistles.
If you've checked the dipstick and are sure you have sufficient oil in the sump, then the sensor is faulty or has become disconnected. You can check for disconnection from under the car - but you'll have to take the undertray off.
The sensor looks like this:
Not difficult to replace should you have to, but all the oil will fall out
One more possibility is that the bonnet switch is faulty, which was pointed out by techie who is a SEAT master tech and therefore knows a lot more than I do about this. His recommendation was;
"Take off the connector behind the drivers side headlamp and bridge the terminals out. This will reset the light. Then get the switch looked at/replaced. "
The reason is that the oil level sensing system looks for evidence that you've opened the bonnet to check the level and resets the warning indication. If it still thinks the level is low, the warning will be triggered again after a few miles.