generally speaking CEL is there for the emissions - i have had that light on my E39 for about 7-8 years, only reset it before the inspection, just to have the light come back couple hours later...
How do you know that the light is solid - did you fire up the engine? was the engine idling rough? sometimes some event would set off the light and the event is gone (may come back later)... it is ok to drive the car in that condition.. but if the light is flashing, that it could be something serious...

tell us more about your condition, and what is happening...